Could a smoke grenade , or an elastic bandage fit inside ?
Looks to once have waterproofing tape around the seam .
Too small I'm afraid, it's about 2" tall and 3/4" in diameter
Bandage maybe ?
Matches? It look similar to the cylindrical Aluminium cigarette tin and there are, more recently, similar pots made of plastic for Lifeboat Matches.
Thanks for the suggestions. Matches might be a possibility, but perhaps from an aircraft survival kit? The standard 44 patt match case was a small brass tin, oval in cross section I believe. It's one of those annoying objects that you recognise, but can't quite put your finger on...