"Do these mylar bags roll or fold small enough to be practical for an Altoid type tin with all the other stuff?"
Borderline. If nothing else, smaller than any decent alternative I know of. (Condoms don't seem like a realistic option to me, because they are too susceptible to puncture, and too hard to fill.)
"What got me thinking was that if I included water purification tablets in my kit that they would be useless without some sort of container to hold the water."
I keep a very tiny (about 1/8 ounce) squeeze bottle of povidone iodine in my mini-altoids tin instead of tablets. I think this will do more purification in less space, and can also be used for disinfecting wounds. It also stores longer, and is less susceptible to damage. In any case, I think that the ability to sterilize drinking water is not a high priority in a typical emergency survival situation. It'll do for now to drink water that will hydrate you, but make you sick in a few days to a few weeks, after you've gotten home. Also, the ability to make fire is a major survival priority; and if you can make fire, you already have a method to sterilize water.
"Can these bags be purcahsed over the internet?"
I'm sure they can, but I don't know of a good source. I have a bunch left over from a business that my mom and brother used to run.
"Evolute:If you read this please be aware that the email address in your user profile does not work. Mail gets returned because of invalid or unknown user."
How do I update my email address in the Bladeforums database? If you want to contact me right now, my email address is:
mikespinak@mac.com