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 made this one a while back for a daytime recon exercise we have planned with a certain unit.