For what, camping or wheeling?
Camping;
First aid kit - for people and animals you might be bringing
Cooking gear - simple, you have to clean what you bring
Trash bags- remember to scrap your food scraps and leave no trace, remember you tooth paste spit is waste too.
waterless hand cleaner
Water for you and everyone, having a filter or purifing tablets is good back up.
Maps of area- duh
chairs and table- make life comfy
lights to set up camp - i put lights on my roof rack not to wheel at night but to set up camp, seems I always get to camp the first night after dark.
Your brain- could be handy
Wheeling;
First aid
water and extra food - shit happens, be prepared
extra clothing (warm) - again shit happens
tools- no not everything, if your transmittion falls out on the ground, you'll probably be walking home. I once read here, service your drivetrain, all the tools you have there take with you. Think about what could stop you, (ex. broken driveshaft, blown fuse, etc.) and take what you need to continue.
Spare parts- how far are you in the bush? That kind question should help you figure out how extensive to bring parts. But belts, hose fixs, tire repair, wire, tape , fuses are basic
Your brain- could be handy, I'm not trying to be condisending, just pointing out planning your trip, knowing when to stop, and using common sence will be one of your best tools
