I've done one cross-country road trip and quite a few 1000+ mile road trips, and I've found fruit to be invaluable, especially grapes and oranges (for their ease of eating). I think it's really easy to get dehydrated while on the road, and the fruit helps prevent that. Plus, fruit goes over well with the kiddos and it doesn't need refrigeration.

As for protein, you could maybe swing some hardboiled eggs the first day (or more if the cooler stays cold enough). Canned fish is another good option for protein. You can either use it to top salads or you could mix it with olive oil or coconut oil and put it on veggies, like bell peppers or celery.

Since the salad you'll be getting on the road doesn't have great lettuce, you could bring a bin of lettuce with you for supplementing what you find on the road. Spinach, boston/butter lettuce, and romaine hold up pretty well.

When we drove across the country we survived on McDonald's salads (topped with chicken, no dressing... so bring your own dressing!) and a meal at Outback. I don't think I would have made it without Outback... the steak and veggies in the middle of the trip really revived me.

For other snacks: of course celery and carrot sticks hold up well and are great munching in the car. If you can make your own root veggie chips, or find a brand that uses good oil, that's a good option, too. And of course jerky and pemmican help a bunch.

If your family eats dairy, cheese is a good option, too. And this isn't exactly paleo, but for keeping adults alert for the drive, I've found dark chocolate covered espresso beans to be helpful. You might also want to bring your own tea bags, because at some of the gas stations the only option for hot beverages is sugary crap.

Pork rinds, pemmican (US Wellness Meats), pre-cooked bacon, assorted canned fish, jerky, nuts, water, and whatever fruit you might like.

I did a 35 hour drive this summer in the south, in mostly 100F weather. Here's what worked for us.

Cold Stuff: My cooler, well packed with ice, stayed very cold. I topped it off with gas station or hotel ice as needed, we also kept only the must-refrigerate stuff in it, and things were still icy after day 3 on the road. I made meatballs with pureed kale and mushrooms that were bite-sized for easy munching while driving. For stops, I made a cold salmon salad with baked salmon, avocado, and lemon juice (ok, maybe a little dicey food-safety wise, but we survived). And a jar of good sauerkraut: Great with the meatballs, and as a supplement to fast-food salads. And hard-boiled eggs of course.

Not so cold stuff: carrots and celery, nuts, dark chocolate, a bag of spinach, apples (pre-sliced but arranged back into apple shape so the don't oxidize, wrapped in plastic), and avocados.

We brought a stack of paper plates and forks - not the most environmentally friendly, but practical for the road and probably still better than stopping at macdonalds. I also portioned out many snacks into small lidded containers for easy grabbing. And of course a good water bottle and a good thermos for everybody.

As I'm writing this, I realize it sounds like a lot of work, but its definitely worth it if it keeps you from feeling awful on the road.

Best of luck!

You can buy small coolers from Koolatron that you plug in the cigarette lighter.

I routinely make the drive from top of the country back down south.

As its a 17-hour drive and my husband isn't paleo, I used to modify fast food to suit my needs. (plus, eventually you will eat a french fry, its inevitable) YUCK

Here is what I am doing these days.

I pack an icy cooler, get a good one that lasts for several days. I also plan ahead and find parks to sit and eat at, so we can stretch our legs a bit. (hey, bring a kettlebell and frisbee!)

Protein: roast beef (I roast an herbed haunch of meat before we go, and we slice as we need w/ mayo (homemade, kept cold, its fine! sometimes mixed with horseradish)

sliced, marinaded and grilled chicken.

canned fish to mix with mayo
hard-boiled eggs

cheese

Veggies:

guacamole

raw celery,
grape tomatoes
all sort of non-lettuce make-ahead salads. anything on this website is guaranteed to be tasty: but this one is really interesting. http://www.theclothesmakethegirl.com/2010/05/27/belly-dance-beet-salad/

roasted in evoo, salt and garlic: bell peppers

bottled water, of course. But if you make it, a quarter of homemade water kefir soda can add some sparkle and keep your system running smoothly while traveling.

The following can be kept out of the cooler

Depending on your carb tolerance: you can make some bars out of dates. These have chia, to keep energy up http://wellnessmama.com/5475/chia-seed-energy-bars/

alternately, you could just buy some lara bars

nut butters, nuts, coconut butter and fruit

if you wanted, to make your road picnics easier, order pure wraps or paleo bread to make sandwiches. Or use lettuce wraps of course.

Just make sure you have facilities to prepare delicious food on the way back too! Good luck