Seem to be having a issue getting the milk from the first dungeon boss. Is it a chance drop or something like that?
You need to find the skill called "Steal", I think that's what it is called. Anyway, the skill allows you to take things from the enemies. Could be more currency for the dungeon, more gold, some materials, but for specific characters, you can take things like Milk. Long story short, find a statue that gives the skill you need, then use it on the enemy.