I'm sure I'm not the first one to think of this, but I'll share it anyway.
The other day I decided to pull apart my C78. This light, like many I guess, has 2 small cutouts in the aluminium heatsink which are used to unscrew it.
Since I didn't have a suitable tool to do this, I decided to make one out of a flat washer.
Simply grind half of it away, or cut it in half with a hacksaw and file the edge flat so it looks like the one on the right.
Hold it in a pair of pliers, and there you have it.
The cutout in the middle means there's plenty of clearance between the tool & the emitter.
First I start off with my small hammer, then the medium hammer, then the big hammer, and for really tough jobs I bring out Big John which is my sledge hammer. Oh and lots of duct tape. :D
Sadly they don't do haemostats which are also incredibly useful.
And all sorts of pliers - the more the merrier. Since you aren't about to apply huge force to anything inside a torch even the cheapest ones will be just fine.
Ages back I did put together a list of useful tools.