Beer.
Well, some other stuff too. Mostly you should be eating carbs, and fruits, grains, and nuts are good for those. If it's warm & you're sweating a fair amount you need to get extra sodium and potassium. Some protein is advised, along with a moderate amount of fat, but nuts and beans can supply these.
In part your "low energy state" will correct itself after you acclimate to the routine. You do, however, need to make an effort to replenish the calories consumed within 2-3 hours.
(I forgot to mention calcium, which may be the most difficult nutrient to get for a vegan, but is needed for muscle energy. Green, leafy veggies are probably your best choice, but inconvenient to eat as "snacks".)