I had a mild episode of this sunday after gaming I'd had a fair amount of bread and grapes, after a breakfast of cereal, but no really substaintal meals that day.
When I got home I finished off some millet pilaf (mostly millet+zuccini) but that didn't help that much. What did help was downing a couple of blocks of smoked tofu.
Before going near-vegan, I'd found that cheese also worked to help me recover. It seems that some (possibly psychosomatic) leaves me needing some kind of salty/protein-rich food.
I have no idea what that could be. (Though I do think I should work on figuring out some portable vegan protein foods). these suggestions might be interesting.
(And I do have to admit I got sloppy enough about the vegan thing that I'm back to vegetarian, though I still try to be mostly vegan).