Looking for portable healthy food

[Not Sure]

I work for a railroad as a freight conductor, which means I'm spending 10-12 hours at a time sitting in a locomotive cab. I work on call, so these trains can run at any time of the day or night. Now, I will get off my butt and do physical activity when we stop the train, such as apply handbrakes, throw switches, etc. and in many cases I get one half to one mile of walking done during this time. But for the most part, I sit in the cab and monitor the train, rail traffic, etc.

I rarely drink sodas - usually just cold water or black hot tea, so I don't have to worry about those calories. Eating, not drinking, is my problem. I've tried getting Subway sandwiches with no mayo or munching on pistachios or eating fruit. I've made my own sandwiches, packed tins of tuna or chicken, even tried a salad once (bad idea - not good when it's not cold). What I really want is portable food that I don't have to keep cold, food that will fill me up, help me stay alert and not gain weight. If I eat the same thing every five days, that's fine with me. I can't do the same thing every day, but when I find favorites I don't have a problem sticking with them.

I'm just at a point where my food/caloric intake vs. exercise/caloric expenditure is unsustainable. And I have a long way to go toward retirement...

Any ideas?