Low Calorie food ideas fo someone who finds it hard to exercise and stuck in a truck all day..?

I work as a truck driver for a mine site and am stuck in a truck for over 12 hours a day (both day and night shift).. Due to the lack of exercise I am able to do now.. as by the time I get home and cook dinner I'm ready for bed. I have gained about 6 kgs, I am hopeful someone can give me some good Ideas af foods I can take in my truck and eat that are both satisfying and low Cal.. At the moment I tend to eat two pieces of fruit a yoghurt and mueslie bar a tin of tuna and two sandwiches over the day and a fruit juice or water to drink.. I cant acces a microwave (the truck doesnt have cigerette lighters either) and I dont have a fridge to use either I just keep a insulated lunch box with a ice brick to keep my food cold.. Thanks in advance for your helpfull ideas :)