For me, this always meant carrying a bulky, expensive kerosene or propane stove which themselves can be something of a pain to get warm enough to use.
There are numerous instructables here on how to make a "Penny Stove." However, there are a series of problems with the Penny Stove concept that need to be addressed. For instance:
1.) You cannot put a large pot on a penny stove without crushing it.
2.) Penny Stoves get very hot, so must be placed on something that will not burn to be used.
3.) Putting a Penny Stove in your pocket or backpack for a hike, it will get crushed fairly quickly.
4.) Penny Stoves are either difficult to light, or do not conserve fuel well.
5.) Penny Stoves are easily blown out in the wind.
As for the commercial "camp" stoves, the *only* ones I've found are either glorified penny stoves (with all the same problems) or require you to carry bulky, heavy, expensive canisters of propane or butane. (Or a mix of the two.) I never did get the point of spending $50 for a "3 oz stove" only to have to carry a 13 oz canister to use it for 1 hour.
Most DIY Camp Stoves I've been able to find use a separate wind screen that's generally a piece of aluminum that would get bent and banged up in my backpack, or no wind screen at all.
All of these issues have been addressed with the new and improved "Penny Stove" or as I like to call it, the "Pocket Sized Camp Stove." I do honestly prefer this over any commercial stove I've yet seen (and I've seen a lot). Better still, it was free. Even a cheap commercial camp stove starts at $30 and goes up quickly from there. I've seen less useful stoves selling for over $100. Considering that commercial stove fuel is also more than twice as expensive as denatured alcohol (calculated by burn time) and harder to come by, there's just simply no reason for me to purchase anything commercial.
While this isn't the size of an Altoids tin, and won't fit in your hip pocket, it will easily carry in a cargo pocket, or in the pocket of your backpack. I keep it in one of the smaller pockets of my ruck sack whenever I go hiking.
For $1.25, you can get a bottle of HEET, and numerous other fuels are even cheaper. (Though I'll tell you from experience, you'll get odd looks buying half a dozen bottles in the middle of the summer. I think the guy thought I was cooking meth.)
Compare this to the Esbit Stove that takes solid state tablets that burn (realistically) for approximately 10 minutes at $0.50 a piece. That's $3/hr, and it's not easy to come by.
While I haven't tested it, I'm pretty sure a $1.25 bottle of HEET (that can be picked up nearly anywhere, including gas stations) lasts me more than an hour.
My preferred fuel is Denatured Alcohol. (See the "Fuel" step.)
Finally, the problem I've had with solid state fuels is the time it takes them to heat up, the amount of heat they put out, and the amount of time it takes to put them away. This stove is ready to go in 1 minute, can be extinguished by blowing it out, or putting the measuring cup over it, and cools off in less than 3 minutes.
For a quick stop to fry up some lunch, this is my stove of choice.
If anyone has suggestions for improvements, I'm all ears.