You don't say the area you are going to be riding in but here is what I must have to travel the forest service roads around my house.
Since I can be a long way from nowhere I have the following.
Check the tool kit that comes with the beast make sure it is complete.
I have a Honda Foreman 450 which has a nice compartment in the back that holds the following nicely.
I large can fix a flat even though my tires are slimmed. 1 quart of oil.( Don't know about the rest of the ATV's if the honda gets low on this it will not run as a saftey feature)
I also tape an extra key to the frame with electrical tape. 50' of good rope along with a decent rachet type of strap that in a pinch you can use to winch if you have to ( Roll over) andDuct tapeall fit in the rear compartment.
Bungee cords strapped to the rack.
And always a full tank of fuel.
I did buy some Gater tires, a winch with plow. I did have some bags on the back but now just bungee a back pack that holds all my hunting needs.
A good double gun/bow finnedrack I also have installed. I also put on some super bright lights as the ones that came with it are a little weak.
Thats my set up anyway and has worked for me.
There is a lot of junk out there that you can put on these things but I just stuck with the stuff I thoughtnecessary and has worked for me for years