Now for a note on software.

First off, you may not be able to use USB Audio, it's very software-specific. If you're using an Android device, it's software version 5.0 (Lollipop) and above comes with USB Audio native. If not, you may need to use a custom ROM or kernal that allows for it. This gets rather tricky and requires rooting the device and voiding your warranty. So, unless you have experience messing with your tablet's software like that, I would recommend you use another method to make audio work for you.

Next, the nice thing about this project is that you can vastly increase your car's functionality with applications designed for your car. For example, the Torque app allows you to install receive your car's diagnostics and engine information from a Bluetooth OBDII scanner that costs about $15. You just plug it into the OBDII port (usually under your dash on the driver's side) and connect it to the app. It's incredibly useful for engine light scans, fuel economy information, even GPS tracking. Which brings me to my next point.

You can also use your tablet as a GPS system. There are many apps out there that offer maps and turn-by-turn navigation instructions. I personally use Google Maps and Navigation. These apps use your tablet's GPS hardware, but are greatly amplified if your tablet is connected to WiFi. Some tablets have 3G or 4G, but mine is WiFi only. Which brings me to my next point.

If you are into rooting and installing custom ROMs on your device, you are probably familiar with WiFi tethering. I use my phone for tethering when my tablet is installed. It allows the tablet to use high-quality GPS, stream music, and give me voice-activated search and notifications. If your data plan supports it, I highly recommend tethering, or a mobile hot spot.

One last note on connectivity: I've found that i wasted some time after plugging in my tablet with turning on all of these apps and getting it ready for a drive. This is where NFC tags are invaluable. They can be used to run pre-programmed tasks just by touching them to your device. I have one NFC tag in my car to turn on and off my phone's WiFi hot spot. I also have a tag on the tablet's mount that turns on the GPS and Bluetooth, as well as starts the car docking app AutoMate. They're very handy and save you tons of time.