The just incase-case is the case of beer you get before
you hit up a bar or a club, so
just in case you want to keep partying you've already got a case of beer awaiting you in the car.
Also prevents you from having to find a
bootlegger and paying double after the stores have closed.
NEL: Dude after the bar lets hit up the strip club
REY: sounds like a plan,lets get a just incase-case so we'll have our
byob taken care of and not have to hit up a
bootlegger!