I've lived in SJ all my life and have lived in downtown for 5+ years now. I quickly made a google map that lists a few places I think Fanime attendees would enjoy. A mix of cheap eats, grocery stores, new hot spots, etc. (No I don't work for any of these establishments, I just enjoy their good food!)
Top of the list, and some of my personal favorites!
Original GravitySome of the best food in DTSJ. Gourmet hot dogs, duck fat fries, I think they still do a mean grilled cheese. Tons of craft beer if you're old enough to drink. Lots of outdoor seating in the back patio. You can still dine in if you're under age. Tell em' Sonny sent you!
San Pedro Square MarketProbably the best place for groups. Tons of options for food, snacks, coffee, etc. Everyone will end up finding something they like and you support the local businesses. Pretty much a big building of food vendors with tons and tons of seating. It's gonna be hot. They have ice cream, nuff said.
JapantownIf you can make it to Japantown (Take the ligh trail or other forms of public transit) it's totally worth it. Tons of places to get your sushi fix, there's a Japanese market for bento boxes or snacks from Japan, Banana crepe serves SHAVED ICE!
https://maps.google.com/maps/ms?msid=206388391728856303611.0004dd53c9347d282ff98&msa=0&ll=37.33653,-121.890049&spn=0.005195,0.009645