bento making

Room temperature bento?

Hey all! First time to the forums and I have a maybe weird-ish question? I'm no stranger to bento making but in the past I have been able to refrigerate and/or heat up my bentos in a microwave. However currently I have a job that not only has NO set schedule, which is bad enough - but I have no access to a fridge, or a microwave. I know I could technically get some ice packs and pack them well, but I have a LOT to carry as a freelance artist, and my bento in a small bag is usually all I can handle. Also I really don't enjoy eating everything freezing cold! Haha I know - so many problems!