Plastic zip-loc bags are a must. Again, not eco-friendly, but if you're trying to eat healthily but at work for hours, pressed for time or trying to dismantle a bomb, you may not have the time to cook a meal.
So, just throw it in a bag.
If you haven't read my entry about flavor building, shame! Read it! Basically, take the main components of a favorite high-calorie meal and transfer it to a lower-calorie dish. Then, put that dish in a bag.
I was talking with my Neg, and this idea came to me when I suggested she make her own granola. Basically, take a high protein bran-like cereal, freeze-dried or dried fruit, roasted lightly salted nuts, and a bit of spice for added flavor, and you've got portable granola. Kind of like making your own chex mix.
Salads are also easy tho throw in a bag, and you're not limited leaf based. I've bagged mixes using broccoli slaw and pasta. Rice could work as well. I also like squirting a bit of lemon (acid!!!) on my salads, fruit salads in particular. Lemon juice is an excellent alternative to salad dressing, doesn't add extra calories, adds vitamin C and keeps produce bright (retards oxidation)
Obviously, there are things you should avoid bagging: usually liquids, cut tomatoes, things that need heavy refrigeration. But, I've found that if I take a smaller bag or, tiny container, I can bag that stuff in my plastic bag. Things that need cold are often bagged with a mini-ice pack to keep them cold.