That was smart to do. Mine are jar candles and I can rig a Sterno stove so it will fit over one and give me a way to warm food if I were to run out of canned heat, which I never will - well, I could sometime after a year.
The very best stove for anyone, to last a lifetime and cook with a small amount of most anything that is biomass, is the “Wood Biomass Stove” that is very heavy and one can cook a meal using several twigs and that's it. That stove is scientific and burns every bit of the small amount of fuel at a high temperature. All that is left is a bit of ash.
It will also use a small amount of charcoal, just a few pieces, and burn every bit of it, again at a high temperature.
I have Kartographer to thank for telling me about this kind of stove. He, of course, made his from scratch, and I bought mine already made.
I have some bushes outside my front door, and could just break off several twigs and that cooks dinner with this stove. Any small pieces of wood from any source is all one needs with this stove. Seashells would also work, any biomass will work.
Yeah, I have one and it is great. We gave one to our son as well. It makes a great present.
Look it up on Amazon. For not much more than a dinner out you can get one and stop worrying about how you will cook or heat water. As you say, it will burn about anything but thrives on small wood like branches you can scavenge and don't need to cut or spilt. The deluxe versions run around $129, but they are well made and should last forever.
Sea shells, probably not. They are almost 100% calcium carbonate (the stuff portland cement is made from).
When you heat them, they break down to a powder, and that is the cement. They’re also good for making Bocci Ball courts :o)