I would be prepared to cook. Plan on carrying some staples with you to get you through the lean areas. Keep in mind what your body needs and come up with some simple, basic meals from easily obtainable ingredients. If you can come up with some grain-based or pasta-based meals that travel well and can supplemented with veggies that you find en route, that might be ideal.

I'm a vegetarian, not a vegan, and I can usually find at least one thing to eat where ever I stop, I don't know if that'd be the case if I were vegan. I already try to keep food on me in case nothing palatable shows up on the road. I imagine with a vegan diet, that'd be doubly necessary. There's stuff in my bag that I hope not to eat, but it looks more and more tasty as time goes by without a decent food stop.

One specific item I've carried is single meal, heat and eat, Indian dishes. I do believe at least some of them are vegan. There are two brands, and neither of them are leaping to mind right now, but I bet someone will come up with them because I probably heard about them here.