I would suggest taking breaks when you can. Add variety to the day...maybe find a way to take a walk (even if it is just around the building).

I have an all day meeting tomorrow from morning into the evening; we have visitors coming to our company. Funny....I feel so tired today in anticipation of tomorrow's meeting and have the same concern about keeping awake tomorrow. I am probably going to be careful not to eat a big lunch and bring some snacks for energy.