I understand why one would think this is a combination of rugsack and backpack. What most
American and Canadian people may not know though, is that these words are not English to begin with. Luggage is "Gepack" in German and bag is "
Sack". A Packsack is the German word for bagage
sack. When searching for the meaning of the word on the
Internet though, I found mostly pictures on German websites of modern bags of the "rollbag" type; a large cylinder shaped sack that can be filled through one end of the cylinder. Then you roll up the
edge of the open cylinder side and lock the ends together with a click lock.
So, in Germany, this word is used for something else than a backpack. A backpack is called "Rugsack" over there.
And in America the word is not just used in Ontario, Canada, I suppose. In Stephen Kings book "The waste lands (The Dark Tower part three)", one of the characters is a young
boy who lives in New York. One morning he packs some stuff: "In the back of his closet, ....., he found the packsack he had worn to grammar
school". He keeps on using the word several times after that, so it must be familiar to people from
Maine too, I guess.