Scouts have worn rolled triangular neckers, or neckerchiefs, since the beginning of the movement. At one time the were more functional, but nowadays they are generally for appearance only. Each group has can adopt their own colours and design, or use one of the available national neckers.
Make Your Own
To make your own group specific neckers, please refer to this article for the proper sizing and construction: http://scoutdocs.ca/Documents/Making_a_Necker.php
Slides, often called woggles, hold the necker in place. These are available at the Scout Shop.
As an alternative, woggle crafts can be made or the necker can be held with a Friendship Knot.
Look smart Scouts! Roll, or fold, neatly. Keep the ends at the same length and you will know the back is centred. Some say to roll the necker 7 times, which represents a good turn every day for a week. (Get it? A good turn... groan.)
The necker is worn over the collar (in contrast to the Boy Scouts of America style of under the collar).
Beaver Scouts put the slide on sideways, making the necker ends stick out sideways. This is known as "whiskers".