First make your meal plan and think through everything you need to prepare and serve each meal.
Think pasta- You need a pot for pasta, a pot for sauce, a strainer for the pasta. Serving utensils, plates and forks.
Think through every meal and compile a food, kitchen, bedding, game lists. We ended up buying double of some things and storing them in the camper to make getting packed up and unpacked easier. We had camper pillows, blankets, dishes, silverware, board games for rainy days.
Then think about setting up the camper:
Flashlights, hammer, things to level it with, wd 40...
I hate to say it but mostly we got out there and almost always "needed" something we didn't have with us. We would pick it up and leave it in there. We camped in our pop up for 10 years before it self destructed.