I collect calligraphy equipment. I do a lot of writing, and every time I see a shiny new nib (a pen tip) or a bottle of brilliantly colored ink, I just HAVE to have it. I use them, eventually. Since I'm wiccan, I use it lots to write in my book of shadows. On that note, I collect herbalism equipment; you know, flasks, beakers, antique looking bottles, and of course the herbs and plants.
I used to collect Warhammer 40k models, and I do have a Space Wolves army, but the hobby has gotten- well- bland. It may yet have it's day again, so I keep them around.