As a Mom to four, 6,5,3,1...I say bring some sort of a stain pre treatment. If you do wash on vacation than great but if not you have a jump on the stain...
As for the car DVD debate, ours is a pop down in our car but it only comes down when we are in the car for over 2 hours or if one of us had to run in a store for something while the other is stuck in the car with the kids...they are happy, healthy well adjusted kids who know not to ask and don't expect it.
If you do go the DVD route while traveling I would have different movies for the drive down and back.
Other gear, a stroller you love and is easy...BABY WIPES 1,000s of them...Clorox wipes for the room and your stroller...night light...glow necklaces from the dollar store...small snacks gold fish, pretzels, cheerios, cheese sticks, yogurts etc for your room when your kids get hungry in the room...rain gear of your choosing...microwavable sterilization bags for pacifiers, bottles, sippy cups etc...hangers...some sort of suction cup for holding toiletries for the entire family or a dollar store hanging shoe organizer for family items (keeps the rooms clean)
Otherwise, bring as little as possible only what you need day in and day out with your family. We will allow our 6 year old to bring is DSi and our 5 year old will bring her Tag and we will have our iPad for some movies we download for us and them.
Am taking a power strip this year too^ thanks for the suggestion....
Enjoy we have 42 more days till our surprise trip for our kids