Great advice on this thread. I didn't see these, and really like:

A little mirror on a flexible wire to see behind things. Helps answer the "is there a bolt I'm not seeing" question.

A long telescoping or magnetic nut grabber (funny combination of words, that). If you drop little metal bits into impossible-to-reach-without-doing-hours-more-work areas like I am prone to do.

I also like a magnetic parts bowl, as I'm also prone to knocking things over. I have (and I know this sounds dorky) a bunch of magnets are handy for keeping things close when working under a car. I like computer hard drive magnets, some are strong enough to hold air tools.u

If, like me, your workspace is a driveway on sunny days, a (pretty strong) folding table is nice. If there are quite a few steps having parts neatly arranged in the order you removed them makes reassembly easier. Actually a table is good no matter where you work.

Don't know if anyone mentioned, but heavy duty blue disposable gloves are great. And the orange gunk for your hands