"I used the cup on one trip with a foil cover in a zip lock but it did not hold much."

Oddly enough, I, too, had been trying to use a sierra cup for the same purpose, getting enough in to brew up a cup of tea. I could sneak in a cube of Esbit, a small wing stove, tea bags and sugar, and enough aluminum foil for an improvised wind screen. I tried to come up with a lid for the cup (a plastic lid from a margarine bowl is precisely the right size, but doesn't stay attached). I ended up putting the whole mess in a zip lock, which at least keeps everything together, but doesn't form a very good package.

How would one go about fabricating an aluminum lid which would affix to the sierra cup so that the whole unit would be self contained? This calls for more mechanical aptitude than I can summon.....