If you fly from a field with nice, low cut grass you can pull about 5 arm lengths of crepe paper off a roll, triple fold the crepe paper at 1 end and use a lightweight yarn to tie the crepe paper to the plane. You can tie the yarn [or string] to the tail boom. A fishing swivel helps to keep the string leader from raveling up. I usually make the string [or yarn] leaders about 10-20 feet long, depending on field conditions. The idea is to get a nice big target out there to discourage aiming at each other's planes. Too much of a streamer will yank the plane when you do hard maneuvers. You could find out what a "rulebook" streamer is from the RCCA web site or AMA rulebook.