Besides the obvious engines and tractors.......
Cast iron toy tractors. Mostly Fordson variations as I got into the old iron hobby because of a Fordson and most of the antique toy tractors that were made are Fordsons.
I also collect oilers for no apparent reason:o Got several boxes of them in the shop. Just can't seem to pass up buying an oiler if the price seems good at the time.
I also collect sparkplugs for no apparent reason:o Got a drawer full of odd sparkplugs and a few that I probably paid too much for. Not sure why I collect them as I don't exhibit them or have a nice display for them.
My wife probably thinks I collect t-shirts as well. I know a couple years ago we boxed up over 100 t-shirts I had that were tractor/engine/show related. I used to buy the t-shirt for every show I attended, but have cut back on doing that as I already have too many.
Also got a drawer full of show buttons that I've kept for some unknown reason.
Of course we also have stamp and coin collections from years ago. I don't consider myself a collector of either, just have what we collected before I got into the old iron hobby.
Guess I'm also a book collector as I've got a pretty good library of hobby related books. This includes most of Wendels original books as well as books from the early 1900's.
I probably collect too many things.