I take leftovers of the dinner before in some form - eg if I'm having steak for dinner I will cook extra and after dinner slice it up and throw it over salad in a tupperware container (I've found dressing in a small sized snaplock bag inside the container of salad is the safest way to transport dressing). Admittedly I have a microwave at work so can take things to heat up which opens up the opportunities quite a lot. But I bought my DD a wide mouthed insulated thermos for her to take warm things to school over winter and that works well for most things (just heat up whatever it is until piping hot in the morning and pack). We've also had a lot of success with her taking egg "muffins", no mess, easy & quick to eat and really filling. Otherwise why not IF during lunch instead of breakfast?