How to eat cheap with a trainer?

Get some microwave food. Microwave use is free at truckstops.
Dollar General, Walmart, etc. has variety of choices of microwave foods that don't have to be refrigerated.
Once you dump the trainer, get a refrigerator and crockpot and have hot meals on the cheap every day.

 

I think it would depend on the trainer, and what is on the truck.
Is there a cooler, microwave, toaster oven, lunchbox oven? A good size inverter or just standard stuff.

How much room do you have to store things in the cooler or in shelves.

At the very least you can get some bread and fixins for sandwiches.
PB&J...
But it all depends on what you have to work with, doesn't it?

 

^^^ Those instant soup in styro thingies, and instant mac n cheese. My kids LOVE those on the fly, easy to tote and nuke.

 

Also, bagels with apple butter.....you can get the single serve apple butters and man, it fills ya up~! Got me hungry now, dangit...

 

And those world famous gourmet Ramen Noodles....yummy!