Notebook
Many quizbowl players use a notebook to write down answers, game scores, clues to remember, or some combination thereof as they play games or practice packets. The notebook allows players to easily flip through many days'/games'/tournaments' worth of notes, track their improvement over time, or otherwise ensure that they don't forget potentially-important clues as they go by.
Some players (such as Seth Teitler) will write down the answers to *every* tossup and bonus part as they go by, and perhaps keep running score beside those tossups. Others will merely write down clues or answers that seem especially pertinent to their knowledge gaps or areas of specialization.
Notebook users should be aware that some tournaments mandate that paper be blank if it is brought into a match, though most TDs and moderators are more lax about this in reality.
The use of products such as Livescribe Smartpens is potentially useful as they can sync audio from a round with notes written on a special notebook.