Until I saw this thread I had no idea that I should be looking into the kind of plastic my container is made of. I guess I just got lucky.

I've been using these children's drink pouches. I just cut off the wings on the cap, fill it with yellow heet, and tuck it inside my Toaks 550. I specifically was looking for a small collapsible container so that I could fit my entire cook kit in the 550. I've used the same container for several weekend trips without any issue, so it seems to be good. :)