i know that there are movie reels in the kino der untoten map. teleport and you can put the reels on the projector and it plays an easter egg. so it could be the same thing- you just have to find the tape player to go with it. i know this wasnt really helpful but atleast iuts something

If you look at it before you pick it up it says it is a piece to a trap.

There are 2 backpacks/trap pieces. Both go on the floor that you start out on in lvl 1. They go on the electricity gates...

One of them is in the bottom floor on the first room on the left once you get out of the elevator. the room with the bowie knife. It is in one of the metal looking lockers that is open.

The other one is on the 2nd floor down, the big control room. It is near the elevator to go down to the bottom floor. If facing the elevator, look to the right of it...it is in a dark corner kind of near some of those control computers or whatever.