I fight sleep sometimes, but USUALLY I can stay awake with only the occasional nodding.
I'm helped by the fact that I often only hunt one morning per week, with the occasional short trip after work in the evenings. Consequently, I can usually avoid the really bad fatigue that sets in from several days straight on stand.
If I am doing a relatively rare all-day hunt, I will plan on taking a nap for 20-30 minutes under a tree somewhere, and that usually helps a lot. Otherwise, if I can't stay sharp, I'll stand up for a bit. I just got a smart phone for the first time back in June, so I also have the back-up back-up plan of reading something on my phone to shake my brain awake.