Don’t put the thing in an easy to remember spot, or an easy to find spot. Put it in an inevitable spot. It has to be physically impossible to leave without it.
Small items can go in front of the door, or put the keys with them, ideally clipped on with a carabiner. Large items have to either block the door, or go in the car ahead of time immediately when I think of it.
Combine this with a wife who is a pro at losing things, and if something is in her way she’ll move it to the nearest open flat surface with no time or reason.