The free trolley from the waterfront to the forts was very helpful. I would highly recommend using it to get around Old San Juan. The tour office was closed that day so we could not get info we might have appreciated.
We walked around Old San Juan to see the Cathedral and Franciscan church. We bought tee shirts (3 for $10) at a shop near all the outlets (Tommy Hilfiger, Coach, etc)
The CVS is really a good place to pick up bottled water to carry with you.
St. Thomas we went shopping in the morning. We got rum for gifts and then collected the charms from the Diamond International shops. It was fun to people watch. I did buy some smaller jewelry pieces (earrings and necklace). We took a ship excursion tour of the island. The views were wonderful but to get to them we needed to pass through souvenir shops and bars.