Are there street carts selling Po Boys (in New Orleans) or are they only at Walk In restaurants?
no street carts selling po boys. They can be had at walk in po boy shops, grocery stores, convenience stores where there are tables & chairs at the first, sometimes at the 2nd & 3rd . . . and you always can get them to go, in which it will be wrapped in butcher paper & likely fastened with masking tape.
And you can get them in regular restaurants too.
IMHO some of the best poor boys in the city can be found at:
3800 Canal St
New Orleans, LA 70119
But with a name like PaddyO, you shouldn't miss this Irish Channel landmark: