I don't mind a veggie sandwich there now and then, it's a good road-trip choice when you need something fast. Unfortunately, not all Subways have all the same offerings but I like trying to combine in flavour profiles like a "Greek" - feta cheese, onion, black olives, tomatoes, green peppers and maybe spinach with a red wine vinaigrette. Or a SW style - avocado, tomato, onion, black olives, jalapenos and maybe a chipotle or sweet onion sauce. "Italian" with mozza cheese, tomato + extra tomato, black olives, onions and maybe an Italian dressing. They aren't perfect but it makes it fun to try and pick something like that. Sometimes I have combos like spinach, carrots, mushrooms with lots of banana peppers.
I'm not crazy about some of their dressings, so usually ask for a small amount or skip them. And for some reason, I hate their pickles. Else I might try a meatless hamburger with cheddar, onion, tomato. lettuce, mayo and pickles.
Edited to add: You can probably tell I don't really like most of their meats, though I don't hate them, either.