There are certain products I buy large quantities of, but I only buy what I actually like, does that make sense? For MAC I love buying nail lacquers and pigments, and I love collecting postcards and promo materials.
In terms of non-MAC makeup, I am a lipgloss whore!
I collect Bonne Bell lip smackers (I have around 300), Bonne Bell lip gloss, and a bunch of other brands such a Bath & Body Works Temptations, C.O. Bigelow, VS Lip Rush, Philosophy, L'oreal colourjuice, Maybelline Shiny-licious, Lancome juicy tubes, etc, etc.
Oh! And I also collect B&BW 2oz. mini lotions