A Triangular bandage (40" x40" x56" is standard) can be used for many things. Mainly as an arm sling. A bandana (mine 22 x 22) isn't large enough for a sling. Do you carry a triangular bandage in your first aid kit? I do not, but am thinking about it. I used to be an EMT and (rightly or wrongly) I am expected to treat others when in a group.
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Jim M