Plague Bags were basically sachets worn around one's neck or dangled from the waist. It was believed that the contents of these bags would protect the wearer against plague, parasites, and miasmata*. 

A sachet is a small bag, cloth, or  pillow filled with herbs, spices, potpourri, or other aromatic ingredients.

Dream Pillows were sachets made with ingredients to promote sleep like hops, chamomile, valerian, skullcap, and lavender.  They were frequently placed next to or under one’s pillow.  Ram's booklet, Little Dodoen (1606), describes how to make a Dream Pillow: "Dry roses, powder of mints and cloves.  Put all these together in a bag and take that to bed with you and it will cause you to sleep, and it is good to smell unto at other times."

*"Miasma" comes from ancient Greek and means "pollution."  Miasma was considered to be a poisonous or evil vapor or mist filled with particles from decomposed matter (miasmata) that caused illness. It could always be identified by its foul smell.