What are good snacks for long road trips?

You could do mini frittatas - assuming you have eggs in the frig! Then use whatever cheeses and/or veggies you have to keep them vegetarian. Would provide some protein and something other than a sweet and they can be eaten at room temperature.

Lots of great ideas here. Along the lines of fresh fruit, I like a fruit salad b/c of the variety it brings, and the fact that it seems a little more "prepared" (and therefore a little more special) than just bringing whole fruit (though I'm not knocking whole fruit at all!). That and, as others have said, some good crackers or bread and cheese, and maybe some walnuts (or maybe walnuts with raisins mixed in)..that sounds like a pretty good spread to me.

One way to avoid a minimum of spilled liquids in the car is fresh fruit, especially now with so many lovely stone fruits, grapes, and the end of the cherries. I agree with Quinciferous about bananas. Clementines are another good choice, easy peeling and they counteract thirst from nuts, cheese and crackers. Keep a couple of ziploc bags in the car and even the banana peels can be quarantined. Deposit the closed bags when you stop for gas,etc.

My family used to do many long car trips. We used to bring
-granola bars
-cheeses, sometimes small packaged ones (like Babybel)
-cut up carrots and celery
-apples and tangerines (can be eaten out of hand/peeled)
-hummus
-bread or crackers
-lots of different dried fruit and nuts
-yogurt cups
-cookies and other small treats

We could go for hours on that spread -- though we'd still usually stop for lunch, to break up the 10-hour driving days.

One other note: bananas seem like a good idea, but they are the worst! They bruise so easily and their peels will make the car smell like rotting bananas for hours. Oranges are also not that great unless they are peel-able.

Hummus, Sprouts, cucumbers, sundried tomatoes, on cocktail rye breads. Put hummus on both sides to protect the bread, rye bread is fairly sturdy and holds up well, dress the sprouts with some oil and vinegar. (or use cheaper bagged mixed salad).
Wassabi Peas are also good--maybe too spicy for the kids and some picky eaters tho.
Some individual "Bento" like flat Tupperware for boxes for the kids. Use paper muffin liners and fill with grapes, carrot/celery sticks,nuts, crackers, Lunch meat (optional), sliced cheese and some dip---ranch maybe if they have cooler with cold packs. Think a 'healthy' type "Snackable" box.
Same for adults with olives---pitted, and cheese.
Hummm..the ranch dip might be too messy..hummus--again.

A recent thread about food for a long plane trip might help: http://www.food52.com/hotline/16190-food-for-a-long-plane-ride

Also, hummus and guacamole can be frozen in plastic containers and work as ice packs as they thaw; carrot sticks and rice crackers can be added for dippers. Homemade granola can be packed with individual yogurts (also frozen to extend duration in cooler), baked tofu or cheese sandwiches, PB&J?

I thought about that! Excellent idea, but I run into a problem of how much do I contribute (monetarily). With baking, it's what I have in the house (a little bit of everything). Sorry, I should have stipulated in the question. I thought about asking her if she'd a) give me money to buy veggies for her (if she doesn't have the time) or if she bought them and I could prepare? Do you think that's reasonable?

Oh, and fresh fruit would be good...

How about hummus and assorted fresh vegetables in addition to your banana bread and oatmeal cookies?