Thanks everyone!
Anna, yeah, it was easy. Because drinking wasn't an option, it wasn't even on my mind. I looked for activities I would love to do - karaoke, comedy, etc. Whether drinks were included or not weren't really an issue for me, I didn't care.
At dinner, our tablemates were usually not drinking - but that's because they spent the day drinking. We were often missing a couple from our table (we had 3) because they were too wasted - that's what they told us the next day anyhow. One night we had the table all to ourselves!!
I was surprised to see that non-alcoholic drinks were being served at some of the activities. I had some of the best fruit drinks ever!!!!!! And others were right, in Old San Juan, you actually had to pay extra to have the rum added in. That was great for me. No one blinked an eye at me, and often on the menu the non-alcoholic version was listed. Very cool.
Sapling: We spent all of our time in Old San Juan. I loved it. We will definitely return to see other parts of the island.