What they do on Valentine's Day.

Kirk-
He'll take you to a romantic restaurant on a new planet. Fancy flowers, nice food, the works.

Chekov-
He'll take you to his quarters and cuddle with you for as long as you want. Lots of kisses and cute whispers involved as well.

McCoy-

McCoy wrote you a poem using quotes from your various favorite books and shows. 

Spock-
He'll take you to a science laboratory and show you a new flower he invented for you by cross breeding.

Sulu-
He'll pick flowers from the plants he grows himself. It's a rare treat since Sulu cares more about his plants than his own life.