I found eating in Hilo to be pretty easy!
Bittersweet blog writes about Le Magic Pan, we went there one day, and their vegan crepe was tasty: http://bittersweetblog.com/2013/02/02/hello-hilo/
I remember eating at a Thai restaurant that was able to prepare vegan food, think it was New Chaing Mai Thai.
Also remember that there were a few Japanese restaurants, where they served veggie rolls, etc, so an option there.
There was one restaurant we went to, a nicer one, that had one vegan menu item… I can't recall the name.. (maybe Full Moon Cafe?) but googling tells me there are a couple, actually, that seem to have vegan options. Hilo Bay Cafe, for instance.
I'm sure you've looked on happy cow, but http://www.happycow.net/north_america/usa/hawaii/hilo/
Definitely hit up the Farmer's Market on one of its big days!
I was there over a year ago, wish I was heading there again soon..! have fun! the botanical garden is gorgeous. so are the rainbow falls. the kaumana caves are worth a visit!
Oh - that reminds me - somewhere on route there is a lovely smoothie stand (the other great thing about hilo, wonderful fresh fruits everywhere!) Go visit What's Shakin' - great smoothies, fruit, and think they have some veg food options, too. But go for the smoothies! https://www.facebook.com/pages/Whats-Sh ... 6174853445