If i'm only to have 1 for the rest of my life, it would have to be more than just a white light, i'd want colors, lasers , trits maybe, ..... lol I do not think anyone makes one like that, I'd have to design and build one myself.
My Nitecore EC11 came with a little plastic tube to take up the extra space if I'm using a 16340 (which is what I use) or CR123A.I’ve wondered that, is there any rattle when using a CR123 in a 18350 tube?
This question is a logical oxymoron. If only one light -- that means that something terribly wrong has happened. SHTF. The most abundant batteries everywhere are AA alcaleaks. So you have the only AA flashlight (any other source of power will exhaust very quickly; remember? -- there is no power supply anywhere) and use alcaleaks that eventually kill your only flashlight. Eh?
So, the only feasible plan would be is to have a bunch of AA lights, not one of them.