Board Thread:The Flash episode discussions/@comment-75.148.114.97-20150401203819/@comment-3481504-20150619235446

Ok, I'd say these three at least as they've been mentioned, are the most highly probable:

1. He has a lot of extremely high caloric food-shakes from the future that he puts in his canteen, which we see him using quite often.

2. He binged on burgers till his time ran out of cows, literally.

3. He eats multiple mountains of food instantly.