I love the Heatstick as much as the next guy, but when those refills run out and you're still stuck in the woods, you're screwed. That's when you'll realize you should have brought a LifeStraw instead.
A Time Magazine Invention of the Year winner, it's like a drinking straw with hidden superpowers. When you use it to sip, it literally cleans the liquid as you go, ensuring you only imbibe potable water even if you drink from a still, gross-looking pond in the middle of the jungle.
The LifeStraw contains no chemicals, uses no batteries and involves no moving parts -- that means, you don't need to worry about adding or fixing anything to make it work. Just pull it out of your bag, stick it in the water source and get your fill to quench that thirst. The only limitation is the efficacy tops out at 1,000 liters of water, so bring a couple of these things if you intend to survive in the jungle for a year to wait out an alien invasion or something. Oh yeah, it has a shelf life of 5 years, too, so stocking is an option.
How effective is it? Meeting full EPA standards for water filtration, it can remove a minimum 99.99999% of waterborne bacteria and a minimum 99.8% of waterborne protozoan parasites, apart from reducing water turbidity by approximately 0.2 microns. It weighs just 2 ounces, too, so you can pack a stash of these in your bag's spare pockets with no problem.
Amazon has the LifeStraw available, priced at $25.49.