Stock up lots of fasteners! When you don't have to always go to the hardware store to fix something, it sure is a nice time saver! When I need a bolt or nut, especially the small ones, I buy lots of them.
I have a fairly good stock of #8 machine screws (A) in a couple lengths with nuts and lock washers. I use these all the time for myriad fabrication and repair projects.
I stock up on drywall screws--they're good for simple wood fastening, home repair, hanging art, and more. I also save lots of small screws (B) which come in handy when doing computer and electronics repair. For auto repair I tend to save every bolt and nut I can (C) because you never know when you need one. This is especially helpful for lug nuts. And I tend to like to save all the wood screws I come across (D).
As for the hoarding of oddball things... particularly rubber and plastic items (E) seem to come in handy all the time.