After clearing the first dungeon (and getting the grappling hook item), capture a fairy in a bottle (or buy a red potion if you're stupid) and head back to the island you started the game on (it is all the way on the bottom row of the overworld, the second square from the left). Locate the old woman then target and use the fairy/red potion bottle on her. Speak to her for a free gold potion. It behaves like a blue potion, but may be used twice. When the gold potion is used up, you can get a free refill by simply speaking to the old woman.