Gryffindor: Do all the things they couldn't do as the other gender. Running around without a shirt for example

Ravenclaw: Studying the new 'anatomy' of their body ayeeee ;)

Hufflepuff: 'Befriend' their already previous friends with their new body, most likely resulting in a few of their friends crushing on them big time...

Slytherin: See how many guys/girls they could pick up in this new body of theirs.