I don't know what it will be like over Thanksgiving, but I would imagine a trip to Old San Juan will be nice, although I would not spend more than an afternoon down there. I'd check out the Bacardi distillery. What hotel will you be at?

I'd also check out the El San Juan Wyndham hotel, its nice, if you gamble there are casino's there. If you can, grab a hotel on the beach. The weather should be nice, and the water will be warm.