I have gotten to the point of making a list of what I need to do on an errand. If I don't write it down, I wont do it. IF I think of an additional item to do while in town, If I don't stop, take out my list and write it down, I inevitably forget to do it. Years ago in my 20-45s age, I never needed a "To Do" list. I could manage dozens of tasks and never forget to do a one of them. Man things in the old noggin have really went downhill fast in the last 26 (almost 27) years.
When working on a project away from my tools, I usually make multiple trips back to my tool box to get an item that I forgot to get the first 3-4 trips. Sometimes, I have to stop and think about what I came after when I get to my tool box. I spend lot of time looking for something that I just laid down on my work table, or did I put it someplace else. When I finally find it, THEN I remember laying it down THERE.
Another annoying thing for me is dropping items like screws and such. The older I get the more fumble fingered I get. I never fail to drop at least one screw or tool when doing a repair. Working off a ladder increases the amount of drops by a factor of 4 at least.