There is some shopping right by the dock or you can take the water taxi for a couple of bucks to the other side. There is a straw market, but I prefer the big building across the street. You can buy banana catsup there too.
There are also some stores on that side. At St Lucia we have done a zipline which I highly recommend and the Brig Unicorn which was okay. I thought the Brig UNicorn was good just because it was used in the Pirates of the Caribbean movies...it was awesome with the sails lowered!