The post-Christmas period is a good time to be unsentimental and declutter.

Never mind the unwanted presents — we all have too much stuff. It becomes even more evident in January when we cannot find space for new gadgets or hanging space for our new clothes. This is an opportunity to give ourselves a windfall and make space. If you are not using it — sell it.

Some FT Money readers may shudder at the thought of using a car boot sale to sell their unwanted stuff. But it is much less time and effort than listing individual items on auction sites.

Do not, however, attempt to car boot your excess stuff until spring arrives. The agony of standing for hours in the cold and rain is a sacrifice too far. But it is well worth going through your cupboards in preparation — Brits spend £1.5bn a year at car boot sales, according to the latest figures.

In the past year, I have followed the fortunes of two car boot regulars. One works for an upmarket travel company and joins with friends and neighbours a couple of times a year to sell surplus clothes, books, albums, tools and kitchen equipment. By combining their efforts they share the time and cost burden, make a modest profit and get rid of vast quantities of junk.

The other was propelled to find money for her first home when her landlord announced she was selling. She had rented for five years and had accumulated many unwanted clothes. By the end of her first day at a boot sale, she made £300.

The Car Boot & Fairs Calendar offers a full list of what is going on all year round. It costs £3 via carbootcalendar.com. Sales often start at 8am — when most business between traders is done. You should not get out any of your better pieces until they have gone. The pitches typically cost £10 and you must take your own foldaway table and possibly a cover on which to present items. You also need clothes rails or coat stands and lots of plastic covers to protect your clothes from mud or rain.

Make sure that you have checked all pockets for any cash or other valuables. You will need to take at least £20 worth of coins so that you can change the notes that shoppers arrive with. Also take lots of plastic carrier bags. Customers rarely have their own, especially since supermarkets stopped giving them away. You can buy 200 for about £2 from Amazon.co.uk. If you have breakable items for sale, you also need paper for wrapping.

It is best to go with a friend, both to stop customers stealing your prize items and also to keep sales going at busy times. You should decide on prices before you go and stick to your reserves. A quick look in charity shops is a good guide to prices. If an item was expensive when new, be prepared to sell online or take it to a vintage or preloved shop if customers fail to make a decent offer (see below).

My experts tell me that by the end of the day almost everything will be sold — including old biscuit tins or tea caddies, children’s toys, old shoes and full bottles of toiletries. Any leftover items can be sold for pennies, or given to your local charity shop.

In most cases, no tax is payable on sales because no profit is made. Yes, you are cashing in on things you no longer want, but you are selling them for less than you paid for them. It is only if you make a business of buying cheap at, say, car boot sales and junk shops and then selling at a profit online on a regular basis that you are deemed to be running a business. From April, “micro-entrepreneurs” will be able to make a profit of £1,000 a year tax-free.

There are some items which may fetch more cash if sold via specialist shops, websites or online auctions. For many women (and a few men), the wardrobe is a good source of unrealised cash. Good quality designer garments that we do not wear can be sold either on eBay or on specialist websites such as Hardlyeverwornit.com.

The provenance of the outfits and the condition is paramount. Clothes I have had for up to 30 years from the likes of Jean Muir, Issey Miyake or Jil Sander can sell for hundreds of pounds. Even preloved Marks and Spencer clothes can fetch between £5 and £10, but rare items such as cashmere coats can go for £70 or more.

Designer handbags are regularly sold at major auctions, although some sellers are distressed to find that their prized Birkin bag is a very good fake when they come to sell.

And sales of vinyl records reached a 25-year high in 2016, with David Bowie topping the charts and Amy Winehouse second. If yours are in good condition, it is worth taking them to a second hand record store — especially if they feature a famous artist who is recently deceased.

It is surprising what you find when you start to search for things to sell. I need to check out the loft to see if the Kate Malone pineapple jug I bought from her north London studio more than 30 years ago is safely wrapped up from the last house move eight years ago. I am told it is now worth a fortune. Fingers crossed.

Lindsay Cook is co-founder of Money Fight Club.com, which offers online resources and consumer workshops. She is co-author of “Money Fight Club: Saving Money One Punch at a Time”, published by Harriman House.