Going on a cruise (cabo!) in 4 hours. What should I definitely do in Cabo San Lucas?

I dont really wanna pay for a shore excursion....they're so overpriced! Anyone been to Cabo and have suggestions? We're there for a day, and I dont wanna drink...I wanna do water sports!!!!!! Is there a place to rent jet skis? How to get to reefs to snorkel...etc...any good shopping? beaches to visit? thx! BTW, Im leaving in 4 hours to get on the plane!!!