I use Pret as my emergency go-to. Only a few items are explicitly labeled as gluten-free at this chain but I often eat the salads, sunshine bowls, boiled eggs, soups, etc, as long as they have no gluten containing ingredients. My bloodwork has stayed fine so I don’t think I’m getting cc’d.
There are a couple of convenient locations at Penn station where I pick up food to eat on the Amtrak train.