At which end of Via Marmorata is Volpetti market located? From ponte Sublicio, how far a walk? Also, anyone know how early in the morning they open. I'm trying to decide if it's a short enough walk from our B&B in Trastevere, to go to Volpetti on the morning we leave for Florence to buy supplies for a picnic on the train.

It's not too far a walk from Ponte Sublicio, but whether or not you have time in the morning depends on just were you're staying in Trastavere and what time your train leaves. Plus, I'm not sure what time they open. Maybe check with your B&B to see if you could put something in their refrigerator, so you could get it the day before you leave.

If you can't get there and back in time for your train, go ahead and buy the evening before. Most cheeses and meats will surely keep overnight unless your room is extremely warm. Bread also, I'd think, though do as Susan says and ask for a little fridge space from your hosts.

Volpetti e fabuloso. Also, Franco (a famed Fodorite) recommends going to the trastevere outdoor market; check to see if it's open that morning. He says they have a GREAT cheese stall.
The Trastevere market is on Piazza di S. Cosimato.

Thanks for the info. On the map it looks about equal distance to Volpetti or the Tratevere market from out B&B, if Volpetti is reasonably close to the bridge. Somehow, I suspect we'll be checking them both out long before the day we leave Rome!

A wise and rewarding plan.