If you own a digital camera, does it have a feature where you can change the default name of the image it saves to? If so, I'd suggest you make good use of it.

Just before your shoot change the settings to something you can understand later on.  Example, I can only change the first two characters of the filename on my camera.  So at the beginning of the day I usually set it to A1.  If I go to several events in a single day, I'd usually go from A1 to A2 to A3 and so forth.  Sometimes it takes a while before I finally remember to burn the images to a CD (end of the week, usually). So the next day I set it to B1. Basically, the first character denotes the day and the second character the event of that day.  Once I get to burn it at the end of the week, I set it back to A1.

Of course, if you can change more than just the first two characters, then you can simply set the prefix to a particular date or even a more understandable shorthand of the event you're attending. As for the frame count, I usually reset it at the end of the day.