Jerky. Jerky, jerky, jerky. It's very dense and very satisfying. I get mine from an organic, no-hormone meat place at the local farmer's market. They even have 2 beef varieties that are no-sugar-added. I feel pretty lucky about that, I know such good options aren't available in lots of places but just get whatever looks the least processed and junky, it's so much better than not having any good protein sources when you're on the go.
When the husband and I go hiking/traveling, for each day we'll be away from home I take a half pound of jerky for each of us, plus a giant ziploc filled with almonds, walnuts, and (in lesser quantity because a little goes a long way) a mix of dried berries. I buy all those things in the bulk section of our grocery store, they are pretty good about carrying things without much preservatives, added sugar, etc.
You can also pack, or depending on where you're going, stop for while on the road, many fresh veggie snacks...bring a jar of almond butter and get celery to go with it...or munch on raw carrots and radishes (tastier than they sound once you start to appreciate the flavor of real foods! plus hunger is the most amazing seasoning). Veggies stay good for at least a couple days even without ice or a cooler!
“The goal of life is to make your heartbeat match the beat of the universe, to match your nature with Nature.” -- Joseph Campbell