Local food worth trying
Vegan haggis with neeps and tatties is the dish to actually order here, Macsween's vegetarian/vegan version (oats, lentils, vegetables, the same spicing as the meat original) is a genuine, long-established Scottish product, not a hiking-trail improvisation, and it's on the menu at the Real Food Cafe in Tyndrum, on the trail itself, as well as in supermarkets the length of the route.
What to buy
Macsween vegan haggis is stocked at Sainsbury's, Morrisons, Waitrose, Co-op and Tesco, worth buying before a night where you're self-catering rather than relying on a pub doing it. Milngavie, at the start, has the widest choice on the whole route (Tesco, M&S, Waitrose, Aldi); Fort William at the end has Morrisons and a Tesco Express.
Good places on the trail
Milngavie: The Honeybee Bakery and Andiamo (Italian, pasta options). Drymen: Beech Tree Cafe Bar, right on the Way, with vegan, vegetarian and gluten-free options, plus Turnip the Beet deli. Balmaha: the Oak Tree Inn, vegan burgers and gluten-free options. Inverarnan: the Drovers Inn, an extensive veggie/vegan menu. Tyndrum: the Real Food Cafe, vegan haggis with peppercorn sauce, tofish and chips, chickpea curry and vegan pastries. Bridge of Orchy: the Bridge of Orchy Hotel lists vegetarian/vegan options. Kingshouse: the Kingshouse Hotel has gluten-free and vegan options. Fort William: The Wildcat Café, fully vegan (tofu scramble, porridge bowl, tofu burrito, vegan cheese on toast).
Trail treats
The Real Food Cafe in Tyndrum bakes its own vegan pastries, blueberry croissant and banana bread turn up regularly, worth timing a stop around on the way through. It's also the rare place on this route doing a proper vegan take on fish and chips (tofish), rather than just a salad.
Where to restock
Milngavie, at the start, is the best-stocked town on the entire route for both fresh food and specialist vegan products. Worth buying more than you think you need here. Tyndrum, roughly the midpoint, is the next reliable resupply, with the Real Food Cafe and a filling-station shop, before the remoter Rannoch Moor and Glencoe stretch. Fort William covers the final stretch.
Things that may not be vegan
Deep-fried vegan items, tofish especially, often share a fryer with meat and fish, and most places do not say either way on the menu. If cross-contamination matters to you, ask when you order rather than assuming it is fine or assuming it is not. Traditional haggis, neeps and tatties served anywhere without the word 'vegan' or 'vegetarian' attached is the animal-product original, not an accidental match.