Both situations happened to me this winter -

a) I was camping about 2 miles from my car. Decided to take a walk in the morning to it to pack some extra gear only to find out that I don't have my keys with me.... Good lord, I found them in my hammock.

b) We were on our last leg about 5 miles left to my car, were crossing a public road and decided to drop our backpacks and sleds and hike light to the car and drive back to pick the gear... I nearly left my outer jacket with the car keys inside that backpack... It would be fun to snowshoes for 5 miles in fresh deep snow only to realize that I need to go back for 5 miles and do it again.

These situations made me think that hiding the keys a short distance off the car a mighty good idea. Besides, there're no valuables in my car, and if anyone wants to steal the car itself, glass window won't stop him.