When dipping an oilskin sack in water, give a unique message “The water runs off the [bag/oilskin sack], leaving it dry.”, which unambiguously identifies the oilskin sack.

Change the material of the oilskin sack to leather.

You can wear an empty bag over your head to blind yourself, but this sets charisma to 6. If you wear an oilskin sack on your head, it starts a strangulation timer. If you wear a bag of tricks on your head, you get YAFM and instadeath, or possibly it just constantly bites your head.