here is another one, although it is not medicinal (as far as I know!)
birch-sap
carve a hole in the birch tree and let the tree sap drip in a canteen (or something else)
then drink the sap
it is very good and tasts sweet
note: dont take more then one litre a day (don't kill that tree!)
when you are done take a branch and press it firmly in the hole so the tree will not bleed to death and the next day, just come back and remove that branch and have some more sap