can easily be turned into slow cookers without the need for ongoing power. They just need to be brought to pressure then well insulated. See Sparrowhawk's DIU idea or the commercially available Wonderbag. Or just wrap the pot in a couple of blankets. This system works brilliantly!
Also consider getting a wide mouthed thermos for cooking. There are several things you can successfully make simply by tossing in the dry ingredients and adding a boiling water
eg oatmeal, quinoa, barley. People have had success with rice, but that has defeated me. Apparently pasta works as well.
We have been enjoying porridge every few days since I started using this technique. Zero fuss, little gas used and minimal washing
Edited to add:
This was the thermos thread discussing other means of slow cooking: