Burritos Sin Fronteras
I lunched at

Although I usually don't feel like crossing the street to photograph the whole burreatery, I only had to take four steps back to get this shot :

I haven't reviewed a burrito truck yet, so this will be the protocol for mobile burrito labs (MBLs) : I'll tell you where I found it. You can try to find it at your own risk. If a truck serves up the best thing ever, I'll go into full-on stalker mode until I have its territory and routine mapped out.
I found it at Telegraph and Bancroft, the Berk. No stalking will be necessary. You can pretty much count on the truck being there when school is in session : it's hard to imagine a spot near bigger throngs of hungry Cal students who want a cheap meal fast.
And boy is this meal cheap. $4.75. Comes with chips, salsa, and, if you feel like taking one, a miniature American flag on a toothpick.
If you have 2 minutes to dash to Barrows, you can probably eat one of these while doing so. If you're more civilized, the bag doubles as a plate :

I have to applaud Gerry's for keepin' it real : they could have mimicked the Yum!-corp burritos these kids grew up with, but instead they deliver authenticity. Thing is, this burrito is really, really, really dry. The only way that could be good is if the meat's thoroughly crispified, and that's not the case here. The only way to salvage the burrito is with a lot of salsa on each bite. I'd refer Cal students in the area down the street to Mario's, but if you absolutely have to grab a burrito from this truck, try to grab four salsa cups along with it.