I've always had a lot of trouble with remembering people, previous actions, and places as well.

Some other people of mentioned the use of the "blond card". That is one I use a lot. I'll even play up how much of a ditz I am in real life so that when something happens it will seem perfectly normal.

One trick I use that hasn't been mentioned yet is the use of "sir" and "ma'am". As a general rule I refer to anyone older than me by those terms. That way when someone pops up and I have no clue who they are it doesn't seem at all strange when I simply refer to them as "sir" or "ma'am."

I hope this helps a little.