Burritos are pretty much the ultimate portable meal: you get beans, guac, rice, cheese and meat all wrapped up in one compact package. The guys at Bay CIty Burrito really get and they have the codiment-to-rice-to-protein ratio down pat with their San Francisco style burritos. Try the Bay City Bomber for a massive package of steak, chicken, beans, rice, cheese, guac and about ten other ingredients. To avoid the post-burrito bloat, the Fisherman's Wharf is a most restrained all-in-one meal that won't leave you exploding.
If you're a picky eater, there's also the option of creating your own burrito.