A backpack/bag/duffel/etc. which contains emergency clothing and hygenics, in the event one cannot go home before going to work/school/see the GF/parents etc. after unexpectedly being up all night partying/doing drugs/banging the mistress/etc.
Matt: Yo man, you gotta work in an hour and we been here blowing llello all night. Won't yo ho know you been up all night when yo go home to change?
Pat: Na, I got it all here in my crack pack.