This is my basic classroom observation kit. I carry these around everywhere. I also use data sheets as well, but sometimes data sheets and data collection systems can be cumbersome. It is good for use in a variety of settings where carrying a clipboard or legal pad around might not be feasible.
The tally counter is very useful for tallying behaviors that occur frequently, occur quickly, and have a clear beginning and end. A counter can be used to count the number of times a student calls out an answer, answers correctly (or incorrectly), gets out of his seat, or throws objects. The list of behaviors you can count with a counter is infinite. (My friends sometimes get annoyed when I bring it to staff development, because that usually means I’m tracking SOMEONE’S behavior).
A stopwatch can be very useful for recording duration (such as how long a tantrum occurs), latency (for example, how long it takes a student to start working after being told to begin), or inter-response times (how much time passes between target behaviors). When I was in the classroom I often kept a stopwatch or timer clipped to my belt.
An index card or small notebook can be very handy for any documentation you want to keep throughout the day from tallies, to times, to basic behavior notes. Anecdotal data may not be the best data to use, but if you have something tangible to look at to refresh your memory it is much better than trying to recall events on your own.