- Trail Mix
- Beef Jerky, Turkey Jerky, Salmon Jerky, etc.
- Freeze dried, or regular dried, fruit.
- Bars (we eat Lara Bars), though the "healthy" of this might be somewhat questionable
Of these, there are those that are healthy, and those that are no so healthy, high/low sodium or fat. But these foods are, in their "natural" state, inherently healthy when not consumed in moderation and as part of a varied diet (my opinion). Not all fat is bad, and I generally buy into the idea that only added sugar is inherently harmful.
Individual packs of trail mix is one of my favorites, and they can be bought at Trader Joe's (organic or not), at somewhat reasonable prices.
What I like to do, however, due to mice getting into our stash (regardless of being vacuum packed in mylar/foil/plastic), is to keep it all in a small/medium bag that we bring to the car when we pack up. If you have no risk of rodents (we live in the country), it may not be worth the trouble. Otherwise, I wouldn't recommend leaving food in your vehicle overnight.