Where do the lifers keep the spare key??
Many people keep a spare key in their wallet, or purse. Some keep it around their neck or ankle. Some people locate one outside their vehicle. I carry my spare in my fanny pack.
I have 5 keys,I gave them to family members so they can next day mail if I need it…
I have a secret spot I taped my extra key to the underside of my jeep.
I’ve seen magnetic keyholders that you can stick underneath.
Personally I’d figure out some way to permanently attach a box (sized like an altoids tin), something that won’t wash away or hit ground in rough terrain. Or open by itself.
For newer cars that have integrated remotes and such, you could have just the key itself replicated and put it in your coin wallet. It won’t start the car as the immobilizer chip isn’t present but at least you’ll get doors open, which could be enough if the actual keys are inside.