Willow water is a very interesting idea. You could also make willow tea which would work faster to extract the active ingredient if you were in a rush.
Willows contain salicin, from which salicyclic acid is derived, which is used to make acetylsalicyclic, a salt, the active ingredient in aspirin, according to my data base. Beware though that newer generations of analgesic products, may not contain this at all.
I know Wintergreen also possesses salicin. So I suppose wintergreen would work as well.