Sleep. Make time to recover and your body will thank you.
That and water, water, water.
Carry your favorite water bottle with you.
If you have to stop at 7/11 for a water, you probably will end up at Starbucks instead and grab a coffee because you are dehydrated and feel sluggish.
You think caffeine will do the trick, but really it will just slow you down more afterward.
Get hydrated and your energy will pick up as well.