I really like the turkey bag idea but I have never used it personally. It merits exploration.
I've never tried boiling in one, and I have my doubts to if it will work- 212F isn't a problem for something designed to handle a 300F oven, but 450F+ of hot rock would probably melt right through the bottom. If you had a way of gaging temperature you'd be ok, but I don't know of anything other than carrying a thermometer. If I'm going to do that, I'm just going to carry a mess tin.
I just use it to carry water in and hold it while the tablets do their thing.
As for mag blocks...
I've probably said these things:
-Scrape with the spine of your blade, not the edge.
-Strike with the spine of your blade, not the edge.
-If you are using a high chromium steel blade, don't be surprised if it defeats you.
-If you have a file in your multitool and didn't use it, don't take it personally if I point and laugh. It's the best way to get the shavings, and it usually is a high enough carbon/low enough chromium that it works well on the ferrorod.
-If you don't have a multitool, attach a bit of hacksaw blade as a scraper- it works almost as well. Or a cut down needle file!
-These aren't made to be used in a hurry, or replaced matches and lighters. These were designed so that you could extend your match supply. Take your time. If you need fire RIGHT NOW, that's what flares are for; if you need fire in a minute or two, that's what matches and lighters are for.