My girl and I went camping for our first time this past memorial day weekend. We tried to think in advance but there were a few things I wish we'd brought... like bacon.
Get a fan and mini light for inside of the tent. My fiance and I went in June and it was HOT in that tent! (Not because we did anything in it...)
+1 on the air mattress. We brought a queen, with sheets and pillows, with a 12V pump. It worked well in a 3-person tent.
Freeze your water bottles before you pack them. You'll probably only need 1 2lb bag of ice for an overnight stay. My 4lbs of ice was mostly ice 5days later in my Coleman extreme.
If you get a coleman extreme, figure out a way to put a handle on it. I used wire rope, grounding lugs, wood screws, and some silicone hose to make a handle. Things are aggravating to open with callous hands.
We brought lunch meat, snacks, and water with some sodas in glass bottles. We bought water in jugs with a pour spout to refill and use to wash our hands.
A small hatchet came in handy, and a rope saw (Has two handles on a toothed bit of wire to cut wood) to prep firewood. Bring some "Local flavor" ads as kindling. You'll have to collect firewood from the trail. We arrived and set up camp first, then went for a trail ride to have some fun and collect fallen wood along the trail. We left the extra at the tent site for others to use after us. If you want to really get fancy, just bring a battery-powered sawzall to help cut things up.
Bring a griddle and a couple of old pots that you don't care about if you really want to cook something. Basic silverware was useful. Bring smores fixins. We just made sandwhiches.
We laid down a heavy tarp under the tent to protect the base of it and our mattress from the ground. I also went to lowes in their rope/chain area and picked up green metal-core stakes that drill into the ground. If you get those, bring a 1/8-1/4" rod (or use the rod it comes with) and a small hammer. Hammer the rod into the soil with a bit sticking out to grab, wiggle it around until it is loose, remove it, THEN put your screw-in stakes in the dry ground. If it's moist, they may drill easily.
We put everything in Hefty bins to help move things in and out of the bronco. Helped to sort and keep track of everything. Dollar general has some decent cheap bins with a green plastic lid that would work well, but they are not sealed from bugs and such that might find their way in.
Oh, and a revolver full of rat shot is a good thing to keep on you.