Depends...
It depends on the event what I do between matches.
If it is a local tourney, I normally spend the time between matches hanging out with my friends and bs'ing about what's going on around us.
For regional events, such as the OB Cues stops, I like to chit-chat with players I don't see often. I like to get on the streaming table and commentate on matches (though I think I mostly BS there too). Within 20-30 min of my match, I like to hit a few rack of balls. If I have time, I will try to get out and get a bite to eat.
At Nationals, I like to go up to the room and hang out. If I have alot of time, I will hit the casino to get my mind off the tournament.
I think for me, the main thing is that I get my mind out of the game between matches. I find that if I don't, by the end of the day, I have worn myself out mentally.