Depends on what's on them. Deli meat and cheese is usually OK for about a day and a half if you pack it with one of those blue ice freezer packs. But, don't put mayo on them. That can be dangerous if it gets to be room temperature for too long. If you want mayo, just raid the bin of individual mayonaise packages at Chic-Fil-A (no refrigeration needed). Same goes for mustard or whatever else you want.

Bring the bread seperately and pack all your meat, cheese, and veggies in another container. Assemble it all in the cockpit and you'll probably be much happier with the result (compared to having a two-day-old sandwich that has been chilled all together...IOW, you have wet bread).

I usually bring other stuff that doesn't need to be kept cool, just to avoid the problem completely.