You should also get an In-Wheel Bearing Greaser Tool so you can periodically re-grease your wheel bearings from home without having to take your machine in to a shop or dealer. And make sure to get one with the hole in it so you don't have to pull anything -- just the calipers and hubs. If not, you'll have to take your axles out as well, and why would you want to do more work than you have to? Ball joints are another part that require a special tool to change. So if you're looking to replace or repair your ball joint, you're going to need a pickle fork.
Other parts of your RZR 4 can be worked on with standard tools that you'll likely find lying around your house or garage. To change your machine's belt, for instance, all you need is an 8mm socket with a ratchet, the spanner/clutch wrench that's included in the factory tool kit, a clean dry belt, and a pair of gloves if you're doing a trailside repair as the clutches will be hot. If you don't have a spanner wrench, a flat head screwdriver can do the trick. Changing the center bearing is also an easy task to complete. All you need is snap ring pliers and an air hammer, they'll come right off.
A little more challenging feat to achieve is a differential rebuild. Before you get started, you might want to open up your differential and see what's going on, as it might be shot on the inside and cheaper in the long run to buy a whole new dif. Either way, there is a plastic cage that holds the lock pins in place, which is a weak point in the system. Replacing this cage with an aluminum one is highly suggested, and can be done with everyday tools that most riders already have.