A good, waterproof tent, down sleeping bag, chair, hot shower...hey, it all fit on the plane. Beer was an issue and has to be solved this trip as the budget is as tight as...
fan, air mattresses, extension cords, sheets and blankets, clothes and toiletries
cell phone
electric skillet is nice if you don't have a camp stove, I have even made biscuits in one before, just flip them halfway through or you burn the bottom. LOL
air mattress (about as good as our sleep number bed lol), some kind of canopy for over the picnic table, cooler with beverages of your choice- especially BEER, cups and/or mugs- even if you buy the refillable one from the TP, bottle opener, swimsuit, beach towel(they don't provide them like they do at the hotels for some reason), snacks, makings for s'mores.
If you're not planning on cooking (we didn't) you may still want to bring some sort of coffee maker. You may be a little far from the trading posts to make getting the refillable mugs convenient to use. My husband didn't want to bring our own beer, and the first day we were there, he and his brother had to go do a beer run. Then we found out we didn't have an opener for the bottles they bought. It was hard to believe, but it was a real search to find one at the trading post. We did end up with a cute Mickey one--the only souvenir my DH bought.