Fig 1. Magnetic tape streamer
(This is a chance to make use of one of those old audio casette tapes.)
The stake is a bamboo satay stick (25cm long, 2mm diameter, about $1 for 50 at grocery stories). Audio casette magnetic tape is used because it is light, tough, cheap, and unaffected by water.
The middle of the streamer, about 60cm of magnetic tape, is tied at the top of a stake (one overhand knot), and then made secure by a dab of glue (eg., from a hot glue gun).
The resulting stakes with streamers are easy to carry (bundled in a ziplock bag) and easy to use.
Fig 2. Streamers in action (leeside eddy, GSD NM, Colorado)