James: Walking along the grounds of Hogwarts and chatting about life and many other things.

Sirius: By walking around Hogwarts, playing pranks on some people and enjoying each others company.

Remus: Taking pictures of different things and studying for your classes.

Peter: Cooking and baking together.

Regulus: Spend time in the prefects bathroom and have some time to relax from the day you have had.

Lily: Studying and catch up in the library while also talking (quietly) about what you are going to do for your next date.

Marlene: Dancing or spending time with each other and sometimes setting up parties in the common rooms.