A slab is a carton of beer, this is regional dialect. Australians haven't the time to say carton when there's beer to be drank, so we say slab. 24 cans, stubbies, etc.
1:Hey mate you comin round for a piss-up Satdy night?
2:Fuck yeah 1:Well make sure you bring a slab!
Where I am from I-95 is the major highway or "SLAB" that I drive on. This can be a SLAB of concrete, SLAB of tar or if u'za back country boy then ur SLAB is a dirtroad. In down South Florida I-95 is my SLAB.
I was ballin' on my way to Tampa and my Brother EROS called. He asked where I was at and I replied "I'm Northboundon the SLAB, bout to hit the turpike".