Three words to remember. Weight, Weight, Weight. Carry what is necessary but don't load it down with anything you don't need. I've seen so many people over my 30 years RVing (we're full timers now) that haul, 8 lawn chairs, 3 lanterns, 50 toys for the kids (you need some toys but not 50), 5 cans of this, 10 cans of that, every tool they've ever owned.....you get the picture. I had a rule when we were recreational RVing. If we didn't use it after 3 outings, out it went. You can lighten your load considerably by using things like plastic dinner ware as opposed to ceramic or glass. Carry "Lynx-Levelers" or something similar as opposed to wood blocks. Don't haul full tanks of water (that's a killer for sure). For the rig itself here's a list:
Basic repair tools, 12v electrical connectors, electrical tape and EXTRA fuses for your trailer (check the fuse block).
A good LED flashlight (or two). Make one of them a backpacking type head-light. Invaluable for hands free work in the dark
Tire tools including TWO good 12 ton bottle jacks and make sure you have the right size lug nut socket for both your truck and your trailer.
Wheel chocks. The mechanical sissor type are the best but a bit more expensive.
Drinking water hose (white), either two 25' or one 50' and an in-line water filter, and a regular hose for washing stuff. Don't use drinking water hose for anything but drinking water.
A hose type pressure regulator (40-50 psi is fine, unless you want to buy a more expensive type than you can adjust to NO MORE than 60 psi)
Good Sewer hose at least 20' with and extra 10' section. Don't be cheap with this one, buy good sewer hose and also get a clear sewer hose adaptor for attachment up at the dump fitting so you can see what is going on when you rinse the tank, and speaking of sewer stuff, don't waste your money on special RV toilet paper or chemicals. If you buy cheap Walmart brand 2-Ply TP and some either "Ridex" or "Dr. Drain" septic treatment, you'll save tons. Don't use 3 or 4 Ply TP in your BW tank as it will clog. If you have girls (more TP is used), rinse the tank every 3-4 days. DON'T let anyone get close to the toilet holding anything small that can fall in there, or store anything small in a cabinet over the toilet. It is most unpleasant, cost wise, to have your tank dropped and cleaned.
If your 5ver is a 50 amp model, get a 50 amp to 30amp adaptor pigtail, and a 30mp to 115 adaptor plug and MOST important of all, if your 5ver has any newer electronics in it, i.e. microwave, stereo, flat screen TV's or if you use your computer....pony up and get a good voltage regulator. A good one is not cheap, $250-$300, but many RV parks have bad electrical spikes, both low and high, and it will frag your electronics and possibly even the entire elec. system in the RV. $250 is a small price compared to that. You can get either hardwired or portable. I use a portable but be sure to lock it to the post with a cable and lock or it'll walk off.
If your 5ver has a generator, keep "Sta-Bil" in the tank, after which, be sure to start it and let so the carb. has stabilized gas in it. You should run it every 4 weeks or so. Un-stabilized gas is only good for about 60 days before it starts to varnish up. Change the oil/filter, and the fuel filter every 150 hours or close to it.
Don't neglect the brakes and the wheel bearings. You'll be....unhappy with the results.
Other stuff you can add or get rid of as you need to. Hope this helps.