I met quite a few vegetarians on my thru-hike of the Appalachian Trail, including some of my hiking partners. In general maintaining a vegetarian diet on a long hike seems to be fairly easy and requires no special preparation. Many traditional backpacker foods are vegetarian and there will be no problems eating in town or at trail magic.
Home in the real world most vegetarian food can often be made vegan with few modifications, and often is not very far off from being vegan.
Unfortunately that’s not the case while hiking. Because of the prevalence of packaged, processed foods among hikers, most vegetarian trail food is heavy on dairy. It’s quite easy for companies to simply add cheese or milk powder to bump up the calories of their products.
This sucks. It can certainly be frustrating when reading package after package and finding that the last ingredient is milk protein on too many items.
My strategy was three-fold. First of all I ate a lot of peanut butter because it’s super high in calories, protein and fat (1 tablespoon = 100 calories!). Second, I looked for foods that weren’t dried. Kashi brand grain mixes were often vegan, had vegetables in them, and were high in protein. Also Indian and Thai dishes that were packaged in their own sauce/gravy. There were many flavors I found that were high in protein and were vegan. My third strategy was to look for natural food sections in grocery stores, which were more prevalent than I anticipated, even in the south. I could usually find dried instant beans there as well as other interesting flavors to add to meals.
Vegan hiking is different from vegetarian hiking, and potentially more challenging. But with some patience and a little extra effort it’s possible to eat well out of regular grocery stores.