A crank flashlight makes it interesting. I am guessing that is about the size & shape of a hand. IE: long and flat, with a crank on the side, which you have to have access to. I also wonder if you are able to bolt something to your handlebars. But OK, radiator hose clamps - cheap & easy to find.
They are flat metal with small slots every quarter inch, and a barrel screw to hold them closed if you can get a few of those, you could strap the flashlight to the handlebars. OR! Just get a package of foot-long plastic zip ties, like they use to tie wires together. They are cheap, and flexible, and easy to use (no tools required). OK, the ideal thing would be make a little box, with a lockable lid, and an open or clear plastic front end (for the light to shine through) . Bolt the box to the handlebars, crank up the flashlight, and off you go. Or you could just super glue the damn thing.