There is a lot of stuff. I'd try overnighting at a local Wal-Mart (make sure the manager and local ordinances allow it), and if you find you need something, there is an easy fix.
Several notable items from me:
1: Assuming you have a 30A connector, buy a 50A and a 20A, as well as the "generator" 30A. That way, if a campsite has a blown 30A outlet, you can use a 50A adapter and still be in business.
2: A generator, or a pair of 2000 watt generators running in parallel. Lots of threads on this on this forum.
3: A decent sewer hose with a 90 degree extension, as well as a clear plastic extension sleeve. The 90 degree extension keeps the hose from dropping down into the sewer pipe, possibly causing a backup, and the sleeve can help you know when tank emptying is done.
4: Depending on tow vehicle, I'd consider a Bolt hitch pin lock. These will key to your truck's key. This is useful because it means one less key to lose, and are decently weather resistant, far better than most locks, especially locks that encounter as much road grit as a pin lock would.
5: BAL X-chocks, Roto-Choks, or another brand. These keep the trailer still, but for safety, I use the cheap rubber/plastic ones as well if the TT is on any type of grade.
6: An electric tongue jack. Helps a lot.
7: A mattress topper. Usually trailer mattresses tend to be low-end, but a topper can remedy that without needing to replace.
