Max's Inventory room is accessed via the purple tube in the leg room (With Sybil in it) which is accessed via the Brain room.
There are 16 objects in the room to check and they are as follows:
-File cabinet
-Employee handbook
-Sock
-Ink ribbon
-Mariachi frogs
-Meatball sandwich
-Ted E. Bear head
-Season one stuff
-Max's Luger
-Roach farm
-Car bomb game
-Bucket of fish
-Maximus shrine
-Balloons
-Chocolate bar
-Spare cables
Press
on each to check them out and the trophy will be yours