I like iPhone notes too because you don't have to worry about having a connection or a signal to get your email open. Just type it in the notes app (which just needs the phone to be charged since it's an offline app), then you can email it to yourself after you're done for a back up copy of it. You can also copy and paste chunks of it pretty easily once you get used to the interface. So I put something like:
Museum Entrance Cashier Name:
Gender:
Hair color:
Hair length:
Height:
Age:
Other characteristics?
Initial Greeting:
Snack Bar Cashier:
Gender:
etc.
Just copy and paste the description prompts from above for each interaction you have you make.
This helps me remember who I still need to interact with as I look for sections that haven't been filled out, and you can always add specific items before you go that you want to be on the lookout for, or add additional text while you're on site if you want to note something unusual or something that will jog your memory later.
Shopper in California's Bay Area