My 2 cents from the EDC perspective.
For many years I'm EDCing in my business suit jacket's inner pocket a cheap stainless steel flask, nicely cut off wide open at the very top.



It is stuffed with disposable plastic rain poncho wrapped around inexpensive 8 Amp hour LiPO battery USB phone charger with glass solar panel on the side, and a tiny AC/DC USB converter on the bottom of the flask. The flask body protects and organizes the fragile equipment and takes virtually no space by itself at all. In emergency it is easy to almost double its capacity simply prying on the concave sidewall outwards, making it a wide mouth SS cup. That makes a way better boiling vessel than anything you could rig from the classic aluminum foil EDC piece. The only caveat - it is noticeably heavier than a piece of foil