Hiya!
I'm staying at the Sheraton Park as well and we also stayed there last year. There are a couple of stores nearby that sell liquor but we've decided to go with Vons and get water/gatorade/liquor delivered to our hotel the day after we arrive. The delivery is free and I've already contacted the hotel and they have no problem with the delivery. They even said they would accept it for us if we weren't there and I made sure to say in my email that there was liquor in the order.
Good luck and maybe we'll cross paths!