First I would ask the company you're renting from what is included. Sometimes they even offer some equipment packages such as linens, BBQ, etc.
For only a 5-day trip I certainly wouldn't buy much. Just take what you'd take for 5 nights in a motel. Then stop at a WalMart for groceries perhaps only breakfast and lunch fixings and have your dinner in a restaurant or take-out just before pulling into the RV park at night. Use paper plates. Perhaps get the boys a game or book for the drive although they probably have their electronic stuff! Don't bother with trying to fix major meals in such a short time.
For your route I'd highly recommend that you travel some secondary roads to see more of this beautiful country. You'll see nothing along the interstates.
Good luck and keep positive thoughts!
