Susan,

Who knows what they coat the inside of beer mini kegs with.
And aluminum containers are cheap to buy.

I admire the re-use and MacGyver creativity; however,
with all the chemicals involved and you are cooking at
high temps, why take a chance.

Lots of workers got sick from working near coal dust,
rock dust, asbestos, cooking oil, lead, mercury, flour, etc.
I think heavy metals are dangerous, and I even avoid tin or
aluminum. All these iron cans are coated with something.

SwampDonkey,
If you are making an Emergency only kit, any of the cans
that might be un-healthy would be OK, if you burn em out.

If this is a regular-use container, I recommend granite
ware with no "warm colors" on the old stuff. Granite ware
teapots, billy pots, bowls, and large cups are cheap and
available, e.g. Walmart camping and cookware sections.

Lighter weight, would be an aluminum pot with teflon,
which is (I think) safe and very easy to keep clean.