Besides the water,  my favorite is the Green Energy. This stuff rocks, and keeps my days filled with energy for productive work. I take some at most 30 minutes before class, for a nice reenergizing rush 30 minutes or so into my practice.

For the Allergy season, to prevent sinus infections, I have recieved great benefit from the use of the Neti pots. If you've never tried these, they are a must for all sinus related issues, best as a preventative measure, but can also help greatly after the sinus buildup has started.