Here's a technique I use when I'm traveling light and don't feel like carrying a stove, or just want to cook up something quick without starting a large fire. It's called a Two Stone or Trappers Stove, and versions of it have been around for a long time. I'll often set it up right in a larger fire ring in the mornings to make coffee and breakfast when I don't want to start a large fire until later.
It's simple and effective, just grab a couple of flat stones of similar size with one flat edge (not from a creek, they can hold pockets of moisture and can explode when heated).
Set up and starting to burn
Bury them partially in the ground and start a fire in between them. Make sure they are stable and strong enough to support whatever pot or pan you're cooking in. I'll test it out with the pot I'm going to use before I start the fire just to make sure. Give it a few minutes for the fire to catch well and build up some coals.
Set your pot on the stones and start cooking. Feed the fire from either side with small sticks and twigs. Make sure you have a good enough supply to keep it going long enough to cook what you need to.
I've found it easier to use this method for quick fires and favor it over using billy hooks or carrying a stove for short trips. It holds the heat in pretty well and is surprisingly efficient, using only small sticks for fuel. If you decide to give it a try, please be safe and pay attention when you're working with fire so you don't burn yourself, never leave a fire unattended and always make sure your fire is completely out before leaving it.