Basically they were French fur traders. They often lived and partly dressed like the woodland Indians. They apparently traded goods in exchange for furs.
However, Coureur De Bois translates to "Runner of the woods". How much trade goods they were able to carry on their backs I have no idea, or how they managed to transport the furs. One could assume they travelled by canoe, but then why the name ruuner of the woods?
There are questions still unanswered and so far I can find no answers.