This is a plea for help. Everytime I see one of the Mexican food carts with umbrellas on 18th St., or at a soccer game on the lake I am dying to try its wares. I lived in Manhattan for a while and lived on street food, so I know it's usually good and authentic stuff. However, I don't speak Spanish, am shy, and there is no menu on the cart. Often times the vendor only has Rubbermaid coolers with unknown (for me) treasures inside.
Is there standard fare for these vendors? What should I never ask for? I am familiar with standard Mexican restaurant fare, but this is new for me. Any helpful hints?