I'm careful about eating while driving but, on long distance trips on straight multilane highways in good weather, I prefer to eat the Jack In The Box "Breakfast Jack". The ham, egg and cheese sandwich on a hamburger bun holds together very well. The cheese seems to keep the rest of it from squishing around as you eat. As a snack, I like crackers.
I would never suggest a hot beverage or soup except at a full and complete stop.
Jack in the Box....memories of food poisoning. UGH. NEVER AGAIN.