Have you ever heard of bento style lunches? It's very popular in Japan, and it's growing in the US. These lunches were intended to be eaten cold. I took a lot of bento lunches in college, and because you use a small container, and pack it tightly together, it works very well. You really don't need anything special, just a container with a tight fitting lid.
Just an example of one of my gluten-free bentos:
leftover grilled chicken
hard boiled egg
small wedge of cheese
Pack the larger items first (rice, chicken, egg) then use the smaller items to plug the holes until the container is full. I use a small 2.5 cup tupperware type container I purchased at Walmart for $2. Yes, there are fancy things, but you don't need them.
If you google "Bento Lunch" you will find tons of sites with ideas. You can easily pack them the night before.