Be very careful not to just take everything and anything "just because". Not knowing what kind of RV you have, everything has weight and its easy to over pack and accumulate too much weight unintentionally.
What we have done for longer trips is we pre-make some dinners at home and freeze them. Its so nice and easy to just take something out of the freezer and put it in a skillet and have an easy dinner after a day of driving. The dollar store has aluminum trays with covers or just vacuum pack them with your Food Saver.
I also went online and ordered the travel guides from all the states we were going to go through. Good resource to have on hand as they have regional maps in them with attractions you might never have considered to visit before.
Do any vehicle maintenance you may need, including the trailer wheel bearings, brake adjustment, to an oil change.
Bring lots of patience and be flexible. Don't try to drive too much/long in a single day.