I fret about these things a lot - so I take pictures on my phone. This completely solves the problem for me and, of course, I never look at the resulting pictures.
Does create some surreal Apple Memories made up of nothing but unplugged plugs and locked doors set to music.... :-)
In my case I very occasionally worry about having left the gas stove on in the kitchen after cooking, and what usually works, in a way similar to the pictures you take I guess, is re-tracing my actions just before and after switching the gas off. This way I can actually visualize how I turned off the gas just before draining the pasta in the sink or whatever.
This works if I remember something particular about that specific occasion tho, but it usually does the thing.