My personal favorites are good 'ol Snickers bars, Tropical blend trail mix from WallyMart, and string cheese. I might throw in some beef jerky on occasion but, although I love the taste, it gets a bit too "chewy" for me esp at rest stops. I have also recently "discovered" bbq Fritos are really tasty and are kept pristine in my spare Nalegene bottle and they also make a nice addition to chili for dinner with cheese (I dehydrate my own from canned - works great!).
I also like to keep WELL hydrated and find Vitalyte works good for taste and extra electrolytes (Cytomax is tastes good at low altitudes but I find it way too sweet up high). The more I'm drinking, the better I feel ie. less headaches, less fatigue, more gas in the tank. The downside is the more frequent stops to relieve oneself