What a wonderful cause! I've taken part in the Relay for Life since 2013, and am just around the corner from my second actual relay. Mine is with the Canadian Cancer Society (CCS) which unfortunately doesn't have it's own listed - but it's a good cause all around. Be sure to support those you know taking part, and help find a cure.
I'm not sure why this is in the fitness category - since I definitely wouldn't recommend it for working out. However, if it's just for a quick boost of energy - this is one of the best. They have all kinds of different flavors and styles. Assault is my favorite. You can also get the original (green) or the import version. Both are also very good. They have some lemonade versions now too. Be sure to find one that sounds the best to you!