Regarding supplies:
Since you’re at a campgrounds and there’s going to be a pop-up there, I’m going to assume there’s going to be a power hook-up. If so, make sure you bring a couple of extension cords, and maybe a power stip.
Regarding tents:
I’d recommend bringing tarps, and a good hundred feet or so of rope. Nothing sucks worse than trying to sleep in a tent that leaks when it’s raining.
Also, when setting up the tent, make sure it is put up properly. The tent roof should be taught, with minimal wrinkles so rainwater can run off the tent. If the ceiling or roof of the tent is loose or has any slack in it, that’s where water can collect. Water that collects WILL find it’s way into a tent.
If you’re in a tent when it rains and you see a “bladder” or water forming on the roof, don’t touch it from inside the tent and push it up to cause it to run off. It’ll leak for sure then. Something about surface tension of the water, and wicking action, and stretching the fibers of the tent, or something like that.
Regarding food:
Freeze bottles of water, and bring those powdered drink stick things for the kids. The frozen water will help keep your coolers cold, and they’ll melt readily enough when they’re out in the sun and you want a cool drink.
If the site does have power, do some pulled-pork in a crock pot. Boston butts are cheap, they take practically no attention to cook one all day (from frozen to done in about 8 hours), and a 6 pound butt can feed six people pulled pork sandwiches for at least two meals.
Save ketchup/mustard packets from fast food places, and bring 'em camping with you. Or grab a handful or two next time you’re at the gas station. Saves on cooler and storage space.
Misc:
Go to the Dollar Store and get some “break and shake” light sticks/necklaces for the kids. They love 'em at night when they’re roasting marshmallows.
ETA: Oh, and thanks to those who mentioned the pre-scrambled eggs trick. Don’t know why we’ve never thought of that, but we’ll be doing that in the future.