I’ve only ever seen bo bia sold from carts like this around Saigon. Bo bia are small rice paper rolls filled with bun (cold white vermicelli noodle), basil, small dried prawns, pickled carrot and raddish, crushed peanuts, chili, lettuce and some slices of slightly sweet ‘red sausage’ called (I think) lap xuong. This vendor keeps all the ingredients in a glass cabinet. She only has a few bo bia on display above her soup vat. Pernickety Saigonese buyers want their purchase daisy fresh. Quite right. Bo bia can suffer heat wilt.
A 5,000VD portion comes with a few greens (if you ask politely) and a bag of tuong. Tuong is a tart, sweet, moderately hot bean sauce used to dip the bo bia into. They’re healthy, they’re a wee bit hot (as in chili hot) and they’re rather light. Definitely a street snack as opposed to a full blown stuffout. However, three bo bia followed by a couple of banana ricewiches and swilled down with a streetside cafe sua da make for an agreeable, if rapid al fresco lunch that still comes in at under a buck. I found this seller on Nguyen Du Street, but keep ’em peeled they’re all over town especially from 5pm(ish).