Since the objective here is preventing the next guy from committing an OOPS!,
I will add the one thing that I didn't really see expanded on.
There was mention of having a chain on the fuel cap, and it is pretty widely agreed that air cleaner covers deserve the same treatment, but what about everything else that may be taken on or off the engine on a semi-regular basis that is not safety chained?
In this case, I refer to the oil filler cap on the valve cover. Was adding oil one time before going out and the phone rang, so I put down the oil and ran to the house to answer the phone . . . . Fast forward twenty minutes, idled up the river, just got on a plane and 1) BAM!! 2) Shut down 3) run to the bow 4) start doing this :scratch:
After looking around at everything, I finally came to the realization that I left the filler cap on top of the air cleaner. Made a nice hole in the side of the cage where it made its direct exit. Luckily it bothered my prop less than it bothered me. Now the cage looks like it has a missing tooth. :lol: Never did fix it . . . now it serves as a reminder.
The simple solution . . . now when I take that cap off, I set it on top of my tachometer which is right next to the key. Then you can't start it without it becoming obvious what you almost forgot. This will work for just about anything temporarily removed from the engine or elsewhere. Also good place to hang plugs if you need to trailer your boat.