Shot glasses, although I haven't bought any new ones in a few years with them all being packed in a box from my move almost 5 years ago. I went through a phase of collecting shot glasses of unusual shapes, sizes and designs.

Other than that, beer bottle caps. I got an idea in my mind to do a wall mosaic using beer bottle tops, so I started collecting them a few years ago. I decided to spend 5 years or so collecting as many as I can and from different brands, different colored tops and different designs. Once I figure out what I have, the fun will really begin... Well, not that emptying all the bottles hasn't been fun... lol