Better take a 2 burner stove, a plastic 5 galloon water container, a small box to hold your eating utensils, a small cooler for perishables! Those styrofoam boxes that they ship frozen steaks in thru the mail, will hold ice for a long time! and, a pottie! Never know when ya will need a pottie! Its a long way between stops in the great out west! And, fuel for the stove, a roll of paper towels, blankets, a pillow, and a tent! Believe me--you'll get mighty tired of being cramped in that mini-van, and by the third night, you'll be looking for a camp ground! And, take some honey and plenty of money, don't stop at fly-by-night repair shops! Go to the dealer of your brand of car! They won't rip you off--other places will! Ask me how i know!!
just some ideas from somebody who has been there, done that! Oh, and something to sit on!

Check Auto Trader, they have a campers section. Check craigslist. Did you check T@B for teardrops, I heard they were reasonable...