Back in the day, I put pizza boxes in a big oversized messenger bag. I thought I was pretty cool.
My SO and I have not had a microwave as long as we've been together...11 years? It's always fun explaining to teenagers that yes, you CAN reheat leftovers/make coffee/make frozen food/etc. without a microwave. The only thing you really can't do is make microwave popcorn, but nobody should eat that anyway.