Many games have consumable items and big inventories. This is especially common in RPGs, where you often accumulate hundreds of knick knacks over your 50 hours of playtime. But this kind of item system has a big impact on your game’s balance.

Risk-averse players will be reluctant to use their items because they don’t know whether those items will be needed in the future. Other players might burn through their items quickly and carelessly, only to find that they can’t complete a difficult encounter later in the game. Some players might even grind for money to max out their inventory, trivialising everything that comes afterwards.

I think I can handle the next battle.

The central problem is that the designer can’t easily predict how many items the player will have at a given point in time. The player also can’t easily predict how many items they will need to complete the game. To provide an appropriate level of challenge to the player, there needs to be some limits placed on their inventory.

Limiting your Bag Size

The simplest solution is to give the player a limited number of inventory slots. This is very popular in survival games, where choosing what supplies to bring with you is part of the core challenge. It also allows for self-expression since different players might bring different items depending on their play-style.

If some items are substantially better than others you could even make them fill multiple slots. Subnautica does this to great effect: your weapons, clothing and other useful tools take up much more space than your food or raw materials.

The major drawback is that once your inventory fills up you’ll need to spend time managing it. Every time you come across a new item you’ll need to open your bag and pick something to throw away. This never feels good, because you’re wasting time faffing about in a menu and also losing some of your loot. I remember this being a particularly annoying problem in Minecraft since it had hundreds of different types of block you could carry.

My inventory is full, and it’s largely full of junk!

Rather than using slots, Skyrim uses a more granular weight system. You can carry plenty of small items but only a handful of heavy ones. This way, players can pick up lots of small items without really worrying about their inventory space.

Unfortunately, the game also has a binary “over encumbered” value. If you’re 1 gram under the weight limit you’ll be totally fine. But if you’re 1 gram over the limit you’ll become over encumbered and your movement slows to a crawl. Since weight is granular, it would have made much more sense for your movement speed to be proportional to your weight.

Limiting your Item Stacks

The Monster Hunter series takes a slightly different approach. You have a big item box that can store a near limitless number of items, just like in most RPGs. But you can only bring a limited number of item types with you on a hunt. This way the player can keep most of their loot at home, while carrying a reasonable number of items in their bag.

Each item also has a maximum stack size depending on how useful that item is. For example, you can carry 10 Potions and 10 Mega Potions but you can only carry 2 Max Potions (a very powerful healing item) and 3 Lifepowders (an item that lets you heal your teammates).

The red numbers indicate you can’t carry any more of that item.

Thematically, it doesn’t make much sense that you can carry 10 Mega Potions but only 2 Max potions (they are roughly the same physical size!) But on a balance level it makes perfect sense. If you have less of an item, that item can be more powerful to make up for it.

This system is less flexible than in Subnautica (you can’t, for example, bring zero Potions and use that extra space to bring 20 Mega Potions) but it’s also more predictable. The designers know how much of each item the player can carry, which in turn lets them set an appropriate level of challenge.

Recharging vs. Consuming

In The Binding Of Isaac you can only carry one item at a time, but this item will slowly recharge. This allows you to use the item repeatedly while also preventing you from spamming it.

The item recharges as you deal damage, rather than over time. This is an elegant solution because it encourages players to get into fights rather than to stand around doing nothing for a while.

This item is fully charged (see the green bar)

That said, I often felt like one item wasn’t enough. The game contains a wide range of items and some of them do pretty obscure things (and these obscure things are never directly explained to you). When I found a new item I often had no idea whether I should keep my current one or grab the new one.

It makes sense that they chose to keep the inventory small. If you had a large number of recharging items you’d probably have trouble keeping track of them all and using them efficiently. In Overwatch, most characters have 3 cooldown abilities and even this can be hard to keep track of sometimes.

Still, I feel like carrying only one item is very restrictive. My item was often on cooldown when I could have really used it and I had to pass over many fun items because I just couldn’t justify carrying them. It would have been nice to have a few more slots.

Loadouts

XCOM 2 uses a hybrid approach where you can unlock items permanently but only use them a certain number of times per mission.

Before you go into a mission, you need to choose the loadout for each of your soldiers. You can give them armour, weapons and a utility item. New options are unlocked by completing particular research projects. For example, you can get new types of grenade with special effects like gas and acid.

Assigning these grenades to a soldier lets them use a small, consumable stack of them in the next mission. After this mission is completed, you’ll still have the grenades unlocked and you can assign them to a different soldier.

Here, “Gas Grenades X1” means “You can equip one soldier with a stack of Gas Grenades per mission”, rather than “You have only 1 Gas Grenade”.

Since your items will refill at the end of the mission, it would clearly be wasteful to not use them all. This encourages players to make good use of their items.

Combining these Ideas

In Patch Quest, my own game, I’ve tried to build an inventory system that’s both simple and flexible.

When you’re at a Checkpoint you can equip a loadout of recharging items. These items can be changed when you reach the next Checkpoint. Some items are more useful in certain regions of the world (for example, the item that cures Soaked damage is more useful at the southern coast where there are many water-type hazards) which encourages the player to regularly switch up their loadout. Preparation is key!

In many rougelike-inspired games your items recharge as you deal damage. But Patch Quest doesn’t contain any weapons (you must tactically maneuver around the wildlife instead of killing it). I’ve therefore made your items recharge based on the distance you travel. Each time you step on a new patch, your cooldowns decrease by 1.

The last 5 patches you’ve stepped on don’t count! This stops the obvious exploit of running back and forth until your items recharge.

You can also pick up one consumable item at a time by stepping on various plants. Below, the player has a Bubble Clove that lets them float for a few turns and avoid ground-based hazards. If the player picks up another consumable item it will replace their current one.

I really wanted to avoid laborious inventory management while also encouraging players to pick up loot and freely use a wide range of items. I think this system strikes a good balance between these concerns, but there are many other ways these ideas could be combined.

Let’s Review

There are almost as many inventory systems as there are games! The kind of system you choose can have a big impact on your balance and also on player enjoyment, so when designing your own system here are some things to consider:

How much can the player carry at one time?

If items recharge, how do they gain charge?

If items are consumable, how do you ensure they always have a reasonable amount?

How often does the player need to manage their inventory? How long does it take?

Is the player encouraged to use items often or to keep them indefinitely?

I hope this article has provided a springboard for you to improve your own inventory system. As always, my articles are only intended as a guide and I’d like to encourage people to experiment and come up with fresh ideas. Game design is still a young discipline, and there’s a great deal of unexplored territory out there.

If you liked this article, why not read some of my other ones (like this one on increasing interactivity by “shrinking” your game).

Advertisement time! Patch Quest’s next major release, the Wildlife Update, is launching next Friday (March 9th). In this update you’ll be given an Exploradex, a nifty handheld device that lets you scan the local wildlife to learn helpful tips.

There’s also a bunch of new areas to explore with new plants and creatures to scan. Here’s a small peek:

The easiest way to be notified is to subscribe to the YouTube channel. In the meantime, you can also get the current version of Patch Quest for free over here. The game automatically updates itself, so this will set you up to receive the Wildlife update too.

Patch Quest has a really small development team (for the most part, it’s only me!) and your support makes a big difference. Thanks again.