I make about a dozen breakfast burritos the night before a trip and freeze them overnight. As someone mentioned before, the ebags cooler doesn't do a very good job of retaining the cold, but with a bag of burritos frozen solid I never have a problem with them staying cold through the day. Then I just stuff them in the mini-fridge freezer overnight and they're good to go the next day. Nuke a couple of them for a few minutes, and you'll be the envy of the crew room on a lunch break.

I also slice up and bag veggies and throw them in my bag too. Cucumbers and jicama are my favorites right now. As long as they're kept in ziploc bags through the day and not left out to sit somewhere, they'll stay relatively cool for a day or two.

The grocery store I go to sells tons of things wholesale, and I've found that corn nuts, at 1.29/lb are an awesome and economical snack. As far as nutritional value, I haven't a clue, but a few handfuls of these on breaks get me through the day.