The lightest cooking fuel adds nothing to your pack weight - that is, if you don't mind gathering fire wood, making a cook fire, and tending to it while cooking your meal. But...if you're lazy like me, or you just hike until you're tired and hungry (OK that sounds more like me!), there's a good chance you prefer a simpler approach.
Delight Sauce. Add enough water to cover your meal by about half an inch, then set aside.
Trail Design's Gram Cracker Esbit stove. Their little 0.10oz stove is great, but since the Esbit fuel turns to liquid while burning, it runs down and fills the deep grooves with fuel which becomes solid when it cools. This creates additional work for you to scrape off the residue before you can disassemble and store the stove. My one piece design eliminates the grooves and almost never needs cleaning. I store it in a tiny MYOG cuben fiber sack to keep the dirty little stove away from everything else in my kitchen.
Trail Designs 1.3 liter Sidewinder Ti-Tri stove leaves me the option to use it as a wood burning stove, which I have as a backup to Esbit. That way I don't need to carry any extra "just in case" fuel.