I love collecting vintage automobilia like emblems, horn buttons, wheel center caps, hubcaps, hood ornaments, sales brochures, advertisements, owners manuals, License plates, and interesting parts from interesting vehicles. I love going to the swap meets (a flea market with a strong focus on car parts, tools, collectibles, etc) which happen twice a year and see what I can find. It really is like a treasure hunt, because you never know what you will find buried in that box or that pile of stuff strewn out on a tarp. Even if I never own the actual vehicles, at least I own a piece of them. With that perspective I probably own a few hundred cars and truck. 
Some of me rare or interesting pieces are;
- A hood emblem off a late 30's Lasalle
- A radiator emblem of a late 20's or early 30's Chevrolet
- A pair of gas tank emblems off a 2003 100th Anniversary Edition Harley Davidson
- A bulldog hood ornament off a 1960's Mack semi truck
- An operators manual for an early 1960's Seagrave fire truck
- A spark plug for a 1960's era airplane jet engine
- A sales brochure for the 1958 Plymouth (the Christine car)
- A hubcap off a 1936-1937 Ford
- An advertisement for a late teens Hupmobile
- A photography book from the 1st or 2nd year Infiniti was around. It was distributed to those who purchased a brand new Infiniti. It even has a letter from the president of Infiniti. My boss from my job in college found this in his local county dump.
I have MANY, MANY more pieces in the collection that I listed here. This is what immediately came to mind.
Vintage is also a key item I sell online in my eCommerce business. You can't find a lot of this stuff in stores nowadays, and there is no guarantee that you will find it at an antique store, flea market, garage sale, etc. When I find the stuff, I feel like I am helping it find a new home with someone who will appreciate it, and for car part I feel that I am helping keep an older vehicle on the road at least for a little while longer. Right now there is a VHS tape from 1990 and a pair of Realistic brand two-way radios (walkie talkies) from the 80's sitting in my mailbox waiting to start their journey to their new homes.