The 10 essentials. After that it depends on the campsite, location, weather probabilities, number of people in the party, etc. etc.
The 10 essentials are a variation of the following. They should apply to any camp opportunity from RVing to backpacking. Some lists combine items so they can include more things, but this is the one that works for me:
1. Water in suitable containers (or a water source and/or a water purification/filtration system.
2. Food in appropriate storage containers.
3. Extra clothing - depending on how often and what you want to change into.
4. Rain gear - could be a poncho, parka, whatever is appropriate for the weather type.
5. First Aid Kit (stocked with what you need - I have all the parts, but no longer carry some things like a snake bite kit. Don't forget insect repellent.
6. Knife (3", much more than that is overkill and a weapon)
7. Flashlight with extra batteries. Windup flashlights help minimize batteries but are kinda large and heavy if you backpack.
8. Firestarter (blocks or paste) and matches (waterproofed).
9. Sunglasses/Sunblock/chapstick. Even in winter!! The snow can wreak havoc on your eyes from glare.
10. Topo Map & compass. For the areas you traverse. You'd be surprised by unexpected rivers & obstructions and a map helps you get around this. A GPS can also be used but most truists still believe you keep the paper maps as well.
I've always wondered why a stove/fuel & cooking utensils have not made the list, but with a firestarter and some meals pretty much self contained, this turns this into a desire not a requirement.
Other things that are not interestingly enough on the list but somewhat necessary are toiletries, and a backpack or dufflebag. Also, not making the list are specific clothing like boots and NO COTTON. Cotton is a terrible fabric in the backwoods. Wool is much better but heavier than some of these fancy fabrics out there.
That's pretty much MY Must-Haves. Everything else is a convenience, nicety, or fun gadget to bring along. I have saved plenty of other persons in the wild because I bring these along.