Since I left Evil Forest, I've been keeping track of which items can be stolen from regular enemies.

Gunitas Basin
(Evil Forest, North Gate, Ice Cavern)
Mu: Potion
Goblin: Potion
Python: Phoenix Pinion, Hi-Potion, Ore, Potion

Ice Cavern
Wyerd: Phoenix Down, Tent, Potion
Flan: Ore, Potion
Cave Imp: Phoenix Down, Potion