[Idiom] rack my sack...

[pinki91]

Hi guys

I have a question about the meaning of "rack my sack", I heard it in the movie "Dumb and Dumber to".

They had a box which they didn't know what is in it. And this is the conversation between them:

1: I wonder what's in this sucker.
2: That thing is worth a fortune! Be careful!
3: It would be nice to know what's in it, though.
1: I've been racking my sack about that.

 

[emsr2d2]

I have never heard that phrase. My best guess is that it's a replacement for the more common "(w)racking my brain" which means "to think very hard about something to try to work it out".