A crate is probably one of the more common additions. Whether for camping, getting work done, or just to hold a few things while you're out riding, this addition fits snuggly on the back of your quad bike. You can buy the best bike accessories through this website http://fitmy4wd.com.au/.
You can find these in a huge variety of sizes with extra clamps and straps to make the crate even more practical. Depending upon how you plan on using the crate will determine what size you need. Regardless of the size, you do get, most models of crates are very sturdy and come with heavy-duty clamps to keep them shut tight.
Another common addition is a winch system. You can use this for doing work out in the woods or to help stranded riders that need a pull out of a ditch. In fact, you'll probably find dozens of uses for these handy tools not just out in the wild, but even at your own home. You can get these installed on the front or back of your vehicle, whichever works best for you. Additionally, you can find other accessories that make use of the winch system such as snowplows, which are great to have around if you ride or live in a snowy area.
There are also a lot of cosmetic additions that you can purchase to improve the look and extend the life of your quad bike. This can be something as basic as wax to protect the paint from all the dirt and other muck that gets on your quad bike as you ride. Or it can be a bit more complex and heavy-duty like an armor plate for the base of your ATV to protect it from impacts that can immediately put any quad bike out of commission immediately.