Since we can get into the nitty-gritty, there are a couple of more specific things.
First, you are likely going to want more grocery items than you can get in the CR convenience store. To that end, I would suggest making a list of groceries you will need for breakfasts, a couple lunches, and at least one dinner. Since you are driving, you can purchase the non-refrigerated items before you leave and bring them with you.
Anything not brought (especially refrigerated items) can be acquired in a couple ways. You can order from Garden Grocer, We Go, etc and have it delivered to the hotel (they will refrigerate the items until you arrive). Another option (less expensive) would be to visit a super market when you stop for gas/the night. If you stop near a Wal Mart or grocery store, you can buy some refrigerated items while others fill the gas tank. You can even make it a racing game. Split the list between the kids and yourself and meet at the checkout counter. Winner and loser get something (winner a prize and loser a chore).
On a personal note, we really like the Purex 3 in 1 laundry sheets:
http://laundry.about.com/od/productreview1/gr/purexlaundrysheets.htm
They have laundry detergent, softener, and act as a dryer sheet in one compact strip. We buy the refill pack, as it is cheaper, and take a few in a (gallon size) zip lock bag. neat, compact, and easy to use. We then save the rest for our next trip, since they are not liquid.
Good luck and have fun!
- Chris