elliebee357 : Most of this has already been mentioned already but here goes. Also, some of this is more appropriate for car-camping (pack everything in the car and park at/near your campsite) rather than backpacking (hike to your campsite with all of your stuff). Both are fun, just very different to prep for.
Clothing: extra socks, flip flops, clothing that can be worn in layers, gloves, hat
Campsite Items: garbage bags (keep them handy), headlamp, wet wipes, toilet paper, extra seating, hammock, dish soap, plastic tablecloth, matches, paper towels
Personal Items: wet wipes, sunscreen, at least one extra gallon of water,
Food: baked potatoes (in aluminum foil, add salt and pepper), soups, PB&J sandwiches, instant coffee (the freeze-dried stuff, just add hot water/milk and cream/sugar), energy bars, fruit
Miscellaneous: If backpacking, make sure to load your backpack correctly! My spouse was miserable on one trip because he put the bear cannister (with food inside) too high in his pack and it made it uncomfortably top-heavy. This is very helpful: https://www.rei.com/learn/expert-advice/loading-backpack.html I cannot overstress the importance of packing your backpack correctly.
From our overnight backpacking trip to Mt. Whitney in 2013: