1. When shit just doesn't go your way...
2. An exclamation of the above, usually accompanied by a swear word.
1. Ever had a day when, from the moment you woke up, things just went gunnysack on you?
2. Oh shit! I spilled my milk! Well that's just gunnysack!
slang for "condom"; prophylactic.
And go pick up some gunnysacks while you're out, you slut!