Agree that you need a short trip before heading out for a longer one. You're not gonna win any races, but just take it slow and easy. I would not rent a car for the family - what's the point of a family trip if you're in 2 vehicles? Carry only minimal water for bathroom stops, like maybe 5 gallons tops. Keep the grocery supply only for a couple of days or so - there is a Walmart most everywhere. Buy in boxes and bags rather then cans - amazing how much weight those canned foods add. Clothing....no more than 4 - 5 days per person since you can run a couple loads of laundry along the way....actually a nice little break at the campground and you meet some great folks. Don't take every tool in your toolbox....look it over and find the commonly needed ones and let it be....Walmart again or Auto Zone handy most everywhere. Minimize. Have a great trip!