Bill--
Typical vegs and aromatics would be one variety of cabbage or another, carrot, bean sprouts, onion, ginger, garlic. I'd likely forgo the sprouts and make coleslaw instead, as the recipe at Rusty's first link does.
To minimize an overy soggy interior I'd salt the cabbage before making the slaw (see
here) and would use only enough dressing to moisten the slaw when mixing.
The pork I'd pull and toss with a little vinegar sauce or vin and a.j. or thiined Q sauce--just enough to moisten it.
Use the procedure at the second link Rusty posted for rolling, however if you're making them in bulk ahead of time, as seems likely, use an egg wash for sealing them: Beat eggs plus 1 t water per egg till well combined. Replace the water called for in the second link with this wash when rolling the rolls--just brush it on
thinly with a pastry brush. Let the rolls dry for 20-30 min before cooking to allow the wash to set. It's best if you can put the rolls on cake cooling racks for air circulation.
If you anticipate a longer time till cooking, allow them to dry in the fridge, on racks and uncovered. Once dried, they can be cooked or frozen or cooked, cooled, then frozen. If you're going to freeze (whether you cook first or not) lay the rolls on pans--with a little space in between them so they're not touching--then freeze. Once frozen, they can be removed from the freezer, packed carefully in freezer containers, Ziplocs, or FoodSaver bags, then place back in the freezer (vac the FoodSaver bags, of course).
Though this process of freezing first before packing usually works quite well, you can guarantee no sticking-together problems if you tuck strips of parchment or freezer paper between the rolls when packing them for freezing.
Note than you can bake the rolls (spray with oil, place on racks over sheetpans, bake in a 375-400 oven till nicely browned) or fry them conventionally. If frying, do not crowd the pot as doing so will cause the oil temp to drop too much--it
must stay above 250. (I'd recommend an oil temp of 375 before frying any rolls and a return to that temp between batches.)
If you're planning on frying them at the festival you can still pre-cook till the rolls are just lightly browned, frying them again till a bit more browned on site.
You could also finish/reheat the rolls on a charcoal or gas grill.
You might consider getting a hold of the little paper boats hot dog vendors use for the dogs they sell. An egg roll or two could be placed in the boat, garnished with a few pickle chips and handed to the customer who could then top with the Q sauce you conveniently placed in squeeze bottles on the counter.