Years ago a good ziplock with a housekey, buried under the dirt at the water meter box was popular. Then it was in a valve box for the sprinklers. Didn't even drop the garage door or lock the doors, vehicles, etc. Heck, we had a tractor that had no key, it was push button start.

Then I moved into town.

Now I suggest a keybox,I personally like the Supra S7..with the rubber cover, looks like a somewhat typical outdoor outlet cover.
I wired mine to the alarm, in case someone knocks it off with a sledge hammer. and there's a tamper switch inside that goes off when it's opened. Just in case someone acquires the combination..they still need a code for the alarm company.

For the vehicle: if you have a good hitch..there's the hitchsafe product.
The following description is probably is not a good idea for those RFID chip type keys.
Using some soap and water, clean up a frame rail top, dry thoroughly, with a hot glue gun, or epoxy (lightly)..glue a key to the top of the rail,
wait for it to dry, cover/blend in with paintable silicone sealant.

then paint with matching(typically black) paint. add dirt for effect.
Pick a couple of drywall screws or nails and hide strategically where you know where they're at, and will not fall out and blow someones tire.
My last truck had 270k on it, and the key was still intact. (and the key was there for 260k of those miles)