Dean
With Dean, things could be interesting. When you both are not on the job you go road tripping. Even though you have to buy every couple hours, it's worth it. Dean couldn't be happier because he gets to spend time with his car and his best girl.

Sam
The occasional past time for Sam and you would be researching and going out for a nice meal. If it was researching, the two of you would be in the bunker while Dean and Cas were out. The both of you would blast music and sing off-key with it. If it was a nice meal, the two of you would just go out to the local diner and have a bite to eat.

Castiel
There was one thing that you and Cas would do during free time and that would getting him to understand everything. Even though it was hard it helped him more with the hunts you both worked on and that was a good thing. You also found it funny when he finally understand something and you could see his eyes light up the slightest bit