In the field, simplicity is best. When I was in the military, in a recon unit, we used to make field gear ourselves. One of the most useful and simpler things we made was this watch cover. It would help prevent light reflection on the watch (it could give our location away).
A simple piece of black elastic. You stretch it to see the time and for 25 cents you can't beat it.
I just made this one for a daytime recon exercise we have planned with a certain unit.
Note: as an FYI, I have a similar thing that is made out of antimagnetic fabric. I'm testing it to see if we can protect mechanical watches from magnetic fields when working in servers rooms, electrical rooms, going through a metal detector, etc.