A car fuels up on gasoline. A human being fuels up on calories. You can extend this beyond the common fuels: She fuels up every day on junk food. That is why she is so fat and ugly. Radical religious groups fuel up on hatred.

fueling up on sugar getting energy by eating a bunch of sugar

To eat or drink hurriedly in order to get back to hacking. "Food-p?" "Yeah, let's fuel up."

Fuel up= get energy

Don't know the meaning of 'to fuel up on', but as for the phrasal verb 'to fuel up', it means 'to eat hurriedly in order to do something more interesting'. For sure, it depends on the context because it's extremely difficult to get at the word taken out of context.