There's a new food trailer on Slaughter at the "Chapparal Food Court" (I think that's what they call it) selling Vietnamese food. I haven't been there yet, but it has a few 5-star reviews on Yelp (not that that means much - the typical Elite <cough> crowd can be a quite useless).
Pho, sandwiches, egg and summer rolls. It's on the south side of Slaughter approximately between Marry Moore and Great Britain (halfway between First and Manchaca). This also makes it the closest restaurant to my house so it gets bonus points already for that AND serving my favorite food (banh mi).
It is the only food trailer there right now. I hope it's good and that it stays because it's about friggin time we had banh mi south of the river (Lulu's doesn't count). I may try it today if they're open when I go by, otherwise it will be very soon at which time I'll report back. Feel free to beat me to it :-)