I believe this idea has some merit but should be directed to a system that automatically heats up your food before you open the can, or when you open it. I envision it as a lever or part you can push, and when you push it it activates a small heating pad that heats the food from inside the can. This is based on the coin-activated heating pads that most of us have probably seen. They are small pads that contain a "coin" or metal piece that can be folded or "clicked", causing it to heat up. This phenomenon uses a supersaturated solution of sodium acetate. Clicking the metal disc releases a small number of crystals of sodium acetate which act as nucleation sites for the crystallization of the sodium acetate into a hydrated salt. Energy is released from the crystal lattice. The heating pack can be placed in boiling water and the sodium acetate can be dissolved again .
I believe this system could be adapted to be part of the inside of the can. Obviously it would have to be in a way in which it cannot be damaged and contaminate the food, so I wonder if there are any non-toxic alternatives. Sodium acetate is definitely not good for the digestive tract but maybe other, non-toxic options already exist. Otherwise the heating pad should be well isolated from the food but still able to transmit enough heat.
Can we find a good alternative? Can we also come up with a design on how to activate the pad before opening the can? Or is it better to do it in a way that opening the can activates the heating? That may cause more energy waste.