... and looking at and photographing ( with some form of scale reference ) the insects found on them is a great way to gather valuable information.

Beyond that, I think an aquarium net is an essential for two distinct approaches. First, to catch and photograph the insects that you have "harvested" by kicking up stuff from the streambed, as opposed to turning over rocks. Second, to sample what in the way of insect life is freely flowing in the stream at any point in time ( not much in the winter but during the season while you are studying or fishing a hatch or multiple hatches ).

Follow the link for reference. A 10" model would be my preference. You can probably find something comparable in a local pet store.

http://www.aquariumguys.com/net12.html

Don't underestimate the value of good pix. Especially if you are tying, and more so if you are creating, your own flies.

John