I trailer my tractors from time to time and I'm always am aware of the key vibrating loose. I remember once when I met a guy half way in Illinois when we traded tractors. I took the key out of my tractor, he didn't. When we met, his key was gone so I put that little tidbit back in my memory. And every since I removed the keys from my tractor after I load them onto the trailer.
On my '89 316, the previous owner had the key tied to the steering column with a piece of twine.
We got some free examples of lanyards at my company from a vendor. There was a metal cable lanyard and a few plastic lanyards. I asked if I could have these lanyards. I will use the plastic lanyards on my other tractors, but they have plastic dashes, so I have to be more careful about installing them. But on my 316, I decided to use the metal cable lanyard. I had a Red Square Wheel Horse keychain, brand new, just lying around, so I thought I would use it also. Sort of matches my black horse Army shoulder patch that I use as my avatar.
I did something similar a few years ago to a Wheel Horse 314-8 that I owned at one time.
Keys do vibrate loose and if you don't put them in your pocket after you load up or have them lanyard to the tractor, you may be keyless when you get to your destination. Not good if you don't have an extra key in your truck.