I put a loop of Home Depot accessory cord on each key, and color code the key/ lock with electrical tape, or paint. When not securing something, the keeper cord gets locked to the lock, and the key rides in the lock. If I'm locking something, I put that keeper loop on my gear shifter for the truck, or keep it with me. Multiple keys, naturally.
Whenever stored, lock it to something. I keep a lock on my chipper chains, and use a lock instead of a pin on my trailers.
Taping an extra set of truck keys under the truck very inconspicuously isn't a bad idea. $.05 of Grey Magic.