Toilette paper. Meeting somebody in the hallway with a toilet roll.. and you knew their destination.
One the house, I soon discovered, there was an unspoken rule about loo paper: Buy some and leave it in the bathroom, and by the end of the day, it would have been used. Put a new one on the next day. Same fate. Try again if you wish. Fate.
So everyone would go to the bathroom with their own roll, and bring it back to their bedroom with them.
Except when one of the boys would stole heavy industrial toilet rolls from the university bathroom, then you were safe for a week or so.. safe from those loo paper encounters.