I've not seen a complete list of the pre-programmed shift functions for the minipac, but you can load the programming utility and should be able to see all of them or change them after moving the jumper.
Here are a few off the top of my head though:
player1 (default shift) + player2 = ESC
player1 + joystick1 right = tab
player1 + joystick1 down = pause
player1 + joystick1 left = return
player1 + joystick1 up = ~ (adjust sound)
Hope it helps.
-Goz