There really aren’t any wine tours in the city itself; you’d have to go way out in Maryland or Virginia for those, and while there are quite a few companies that do private and semi-private tours, you’re looking at at least 5 hours round trip, which would probably only give enough time for 2-3 wineries if that. It would make for a painfully long day to do a VA/MD winery tour then dinner then drinks, especially if half that daytime timeframe was spent riding on a bus.
Capital Yacht Charters does private and public events: http://www.capitalyacht.com/index.php Their prices to charter an entire boat are probably quite high but you may be able to line up with one of their public booze cruises; these are often held around dinner time though, so you might need to do lunch instead of dinner. Note: if you go there, park at the mandarin oriental hotel and walk over the pedestrian bridge to the marina, as it’s a real biatch to find the marina by car.
There is a Kimpton hotel in Old Town Alexandria (I forget its name but google will tell you) that has a spa onsite; they will book you a “day use suite” and plan a spa day for you. Depending on the size of the group, the suite would either just be used for lounging in between treatments, or can be turned into a private nail spa, so girls go downstairs for massage/facials and get a mani/pedi in the suite. You get the spa from 9-5 I believe. No idea on the cost as my friends booked this as my bachelorette adn they paid for it all.
If the time of year is right, a trip to the baseball game would be a lot of fun. They sell a premium seat package for the “PNC Diamond Club” and I’ll be honest, the tickets are pricey, but they get you some of the best seats in the ballpark plus free beer delivered to your seat, and a pre-game buffet, candy bar, popcorn bar, lounge and more free drinks.
Living Social has a building at 9th and F NW where they do all sorts of classes like oil painting, candy making, cheese tasting, and there’s almost always wine or beer involved so a little class together might be fun.
One of the Hilton hotels in the city is said to have a fantastic rooftop pool deck, and you can buy day passes even if you’re not staying in the city. I’m not sure which Hilton this is— I don’t like public swimming pools so I never bothered to find out— but I think it’s the one on Connecticut Avenue near Adams Morgan, at any rate it is a Hilton so a few calls should turn up the right hotel.