Re: hoarding. (If anyone still cares.) I'm not much of a "hoarder", but I do have a few collections, some large, others (mostly) small. I put an upper limit on my collections, which means I tend to collect up in one thing and then move on.
Among them:
-- Reference books. Particularly math/science reference books. My favorite is "A Million Random Digits with 100,000 Normal Deviates" by the Rand Corporation (1955). I can't say it gets much practical use, but I just love the premise: a huge book full of high-quality random numbers.
-- Other books. I love to read and I'm a lightweight bibliophile.
-- Calculators. Particularly HP calculators. Particularly the Voyager line (particularly the HP 12c, 15c, 16c; I have a pair of each of these for home and work), and the 48sx and its software cards. Plus related literature for all of the above.
-- Slide Rules. Particularly Pickett slide rules. (Toys are made of plastic. Tools are made of metal.)
-- Here's a weird one: AC cables. I used to do a lot of global travel for work. (Now I travel much less, albeit usually for pleasure.) For fun I would pick up a standard/universal AC cable (like the kind that will plug into the back of your monitor or PC power supply) whenever I went someplace that had a different plug design. So far I have: Americas, UK, Europe, South Africa, Australia/Asia, India, Denmark, Switzerland.
I used to hoard more than this, including arcade video games. That was a timesink and a half, plus my collection of 20+ games took up appx. 400 square feet. (It's amazing what you'll get rid of when you get married.)