Last time I did an amusement park it was a long time ago. I used a digital voice recorder to record the conversations (legal in our state) and made notes in a corner somewhere after each concession stand interaction. For rides, I got the descriptions of everyone while waiting in line so all I had to do was look for a name and write what was discussed.
Like someone else mentioned, I use my cell phone and text the information now. My cell allows me to write a text and not send it but it'll save. So what I do for my restaurant shops is write in the pertinent information needed. Then I plug in times, names descriptions, and so on as needed.
For descriptions, I have a system. I note the race, age, height, weight, hair color, length, and style, glasses or not, facial hair or not. I always note it in the same order so I'm in the habit and don't forget. For taking notes, I use a type of shorthand: CM,23,511,190,scbr,g,nf. You can probably figure it out but that would mean a Caucasian male, aged 23, 5'11" tall, about 190 lbs, with short, curly brown hair, wearing glasses, and no facial hair. The first is a lot quicker, which is important when time and being inconspicuous are important.
Hope that helps.