I have a trick that works for such things (at least for me).

When I'm leaving keys I imagine myself going back and searching for them and remembering that I left them there.

Then when I really am in this situation I remember the false memory and find them :)

Same thing works with remembering to buy something when going back from work and other "do THIS when THAT". When I decide I have to buy X I imagine myself stepping out of the bus, going up the stairs, remembering to go to the shop, turning and going there.

Then when I really do this I remember to turn :) What's funny is that a few times I then decided to go out on the next stop (a little longer walk but less mud when it's raining) - and I haven't remembered because the trigger didn't happen :)