Lyric discussion by ncomase 

Cover art for Junk lyrics by Paul McCartney

This is simply a breakup song. Paul goes over the things shared by the couple (cars, bikes, things that they only would understand the sentimental meaning of) and how they purchased them together ("Buy! Buy!...") and now that they've broken up, they're just junk in the yard, either tossed away, or more likely for sale ("Why? Why?...").