My answer from this thread: http://paleohacks.com/questions/96805/suggestions-for-lunches-eaten-cold/96832#96832
I like to take frozen shrimp/prawns and put them in a container. That way, they defrost during the day, but still stay cold enough that they are safe to eat by lunch time. I usually put some lime juice, chipotle, and olive oil in there too, to get flavour going. Then, I just slice open an avocado (another reason to carry a swiss army knife at all times), and combine the shrimp and avocado. One of my favourite, absolute easiest lunches.
Another lunch I like is filling a container with leftover beef, finely chopped peppers, bean sprouts (if you eat that kind of thing), julienne carrots/zuchinni, fresh ginger, chopped garlic, etc, and then bringing a thermos of bone broth to pour over the whole lot- it is half cold lunch, half hot lunch, no microwave or stove top required!
For salads, I'm picky and hate the "soggy" and kind of lose the point of eating all those leaves when there is no yummy dressing, so I pack one container that SEALS really well, and put all the "extra" veggies (carrot, pepper etc), meat, and dressing (some variation involving lime/lemon, balsamic, olive oil, or sesame oil). This way the meat soaks up the dressing too, which is always a good idea. I usually have a little container for "crunchies" that would otherwise get soggy, such as seeds/nuts. Then, I just have a big container of lettuce/greens. Invert both the containers into the big container, put the lid on, shake well, and proceed to enjoy!
Another great one is just little containers of leftovers- a hardboiled egg (coat in sausage meat and fry for extra calories), some roasted squash, an avocado (again, swiss army knife is key), a couple slices of cooled bacon, leftover sausage, chunks of cheese, containers of yogurt with berries (if you have a sweet tooth!), and thermoses with whatever you ate for dinner the night before. Easy, and all the little bits add up to a substantial meal.