The only vegan sandwiches I have "bought" from a grocery have been those at progressive alternative healthfood stores that have a deli with labeled vegan sandwiches. One was a quinoa, raisin, carrot type sandwich. Often is is hummus, olive, cucumber sandwiches. Once at a restaurant I had a tempeh lettuce tomato and vegan mayo sandwich. Otherwise there are a ton of different vegan commercial burger patties out there. In the U.S. Bocca burgers are popular, and there is Amy's products, Dr. Praegers, Field Roast, Beyond Meat, Gardenburger, and others. I have had frozen Amy's vegan burritos. They even have a gluten free vegan burrito. for bread, I buy vegan hot dog and hamburger buns from Rudi's Organic bakery bread brand (not all their bread is vegan but many are). I also use Ezekiel and Food for Life bread. Otherwise, more often than not, I make my own bread and tortillas and buns.
Some sandwiches I commonly make:
sliced avocado, sliced tomato, black pepper, onion slice
sliced tempeh, sauteed savoy cabbage, sauerkraut sandwiches
tons of homemade bean burgers (my favorite is white bean, shredded carrot, cornmeal, chive patties), often with vegan mayo or just lettuce and tomato etc
hummus, olive, red pepper, sprouts
peanut butter and banana or apple or raisin
chickpea salad sandwich with Just Mayo vegan mayo, black pepper, mashed chicpeas, celery, onion
pizza sandwiches: black olives, roasted pepper, roasted onion, tomato paste, mushroom on toasted bun
roasted chickpea, pineapple, yellow squash, bell pepper with pineapple mustard sauce all in a ciabetta toasted bun
broiled marinaded in liquid smoke and soy sauce portobello mushroom and onion sandwich, sometimes with vegan mayo
homemade falafal patties
Sweet potato, kale, black bean burrito
canned fat free refried pinto beans, brown rice, diced tomato or salsa wrapped in a burrito with spices like cumin, chili powder, garlic powder, paprika