I'm not sure what it's for, but I HAD to have it

There's times in my thrifting adventures that I come across something that I'm at a total loss as to what it's for. Case in point... this red vinyl bag.

That red vinyl is what caught my eye.  It's got a lovely triangular shape, it's in fairly good condition with just a couple scuffs and scrapes and did I mention the BRIGHT RED vinyl.  The zipper works perfectly, too.  Then when you flip it over you have this...

Hmmmmm, I wonder what you're supposed to put in there???  My first thought was a tennis racket bag, but I don't think that's right.  I'm gonna figure out something cool to use my rad red bag for!  I'd be happy for any suggestions!!