If you're planning on cooking most of your meals, consider bringing a small portable gas grill and a couple of 1 pound propane cylinders. It will expand your menu options some and (perhaps more importantly) expand your kitchen space some by moving some of the cooking outside. The $20 specials are functional, though predictably not as good as $100+ Webbers or whatever. With many of the small grills (at least the cheap ones) it's nearly essential to keep the lid closed as much as practical to keep the heat up.
Also figure out what furnishings if any are included in the rental. You'll likely need to bring some kitchen and dining things (maybe everything you're likely to use), and maybe some bedding, cleaning supplies, etc. As you'll likely want to eat outside much of the time, a tablecloth for the picnic table would not be a bad idea. Likewise a welcome mat to scrub off shoes will help keep dirt down inside.
A couple of aim-n-flame lighters are probably a near essential. Many RV stoves don't have any built-in lighter.
Make sure everybody in your family knows how to open all the doors and emergency exits, and understands that in the event of a fire they need to get out immediately and not worry about trying to save anything. Remind them that the back window exit, although close to floor level inside, is something like five feet off the ground outside and so diving out headfirst is a bad idea. Also make sure they understand the rudiments of the plumbing (i.e. how to flush the toilet and how to turn the water pump on and off).
Sounds like it will be a marvelous trip!
