Driving 10 hours to a family reunion of 17 people and need a transportable dessert that will need to survive in the car with lots of supplies. Help!

Homemade cookies, bars and watermelon.

Id bring a well wrapped Bundt Cake! Something like this:

http://www.thenaptimechef.com/2011/07/portable-chocolate-peanut-butter-swirl-bundt-cake-naptime-everyday/

(1) watermelon (2)if you have access to a charcoal grill or a firepit, smores. You can upgrade the chocolate to dark or bittersweet if you like (3)pound cake. It will improve if you make it a couple of days ahead. You can transport it in loaf pans, so it should be safe. If you are outside, just slice it and people can eat it with their fingers. If it's a sitdown meal you can add some ice cream or fruit when you get there. James Beard has a recipe for a food processor version that's fast to make.

if there is a reliable and decent store near to the reunion, maybe you could go onto their website, call them and order something for that day. i have done same for holiday dinners when i was traveling (and i have also traveled in car with cooler and foodstuffs) but to be able to pick up a premade quiche and serve it the next day for the holiday crowd, in my case, was a time and life saver. have fun with the relatives!

on further thought...Keep the pie, baklava idea..and add something fun purchased.
I'd go with MoonPies...http://www.amazon.com/Moon-Pie-Mini-Variety-count/dp/B004CH7WJE

And some other fun 'retro' candy like you'd get at Halloween in the 70's.
http://www.groovycandies.com/pc/retrocandy.asp?_vsrefdom=paidsearch&gclid=CLy2kdm4hsYCFUo8gQodmWwAcg

I'll bet you hit some memories with a bag of 60's and 70's style candies. Oh...oh..wax lips.

Just make sure they're stored in the cool for the trip.

Baklava.
Pecan Pie.
Cookies, Brownies..