Activated charcoal

Can't imagine what you are eating at a fast food place (vegetarian or not) that could be remotely healthy. Taco Bell can "make do" in a very desperate situation, but that's about it! Leaving off the meat still leaves... white bread? mayonaisse sauces? fried foods? Or those horrid preservative lettuce, cheese, and scary dressing salads?

Take activated charcoal/bentonite/montmorillonite (with water on an empty stomach), it should absorb any toxins (bacteria) you might have ingested. Good for mild food poisoning, and toxins in general.

The ACV suggestion is good, too.