Any suggestions on storing all our luggage at a train station (Naples specifically) for a day trip to Pompeii?
Bob don't know about baggage storage at Naples Train station--would imagine there is one--but be VERY careful we got involved (5yrs ago) with a sort of scam at the Naples train station while transferring to the smaller train going to Sorrento (same way you would be going) when a man who looked like he worked in the station pointed us in the right direction to the local train (downstairs) but also must have alerted some helpful man to carry our luggage downstairs to the platform and then tried to charge us about $25 dollars for doing so, my husband told him that we did not have that sum and he would not give up our bag unless we gave him something I think he gave it up for something like 10 Euros in the end--be careful and lucky you Pompeii is wonderful--they might even have something there to held your luggage at the station.
Most large train stations in Italy have staffed luggage storage areas. No lockers. The Trenitalia website does show a "Deposito Bagagli" at Naples centrale. We used the ones at Pisa and Florence and they were great and quite safe. We have no experience with the one at Naples.
I've left luggage at the Naples train station. If you're facing the train station proper from the tracks the luggage room is on the far right, if I remember correctly. Just look for the big sign that says "deposito bagagli".
Here is a link to further info on charges and hours: http://www.raileurope.com/us/train_stations/naples.htm#services