I just flew delta this week & requested a "vegetarian" meal. "Vegetarian" means vegan - "lacto-ovo vegetarian" is the only other veg choice.
Here is what I had:
Portland --> Dallas: bagel w/Promise margarine & strawberry jam, corn flakes, soy milk, banana.
Dallas --> Boston: grilled veg sandwich (dunno if the bread was vegan), cape cod potato chips (mmm!), red apple, bag of raisins
On my way back...
Boston --> Atlanta: pretzels
Atlanta --> Portland: The flight offered food to purchase!! So I bought some food in the airport but it was nearly impossible to find anything vegan. I ended up buying an onion bagel, plain, and a "salad" (which was that iceberg lettuce salad mix in a bowl with lite italian dressing).
On the flight, they sold food from some catering company - it was not vegan at all. The three sandwich choices were a club, turkey, or beef sandwich. They had cookies or cake you could buy. They did have one salad but it was not vegan - it had cheese in it. Not to mention it was $8.
So be sure to ask at the gate if food is served - you might have to get something in the terminal. Also, don't forget to call 48 hours in advance to make sure they have you listed as pure vegetarian!!