You can find nice upgrades for your party in Mythril after you get an airship, but don't go crazy right away, because nothing here can be used in the Magnetic Cavern. If you have money to spare, by all means buy upgrades (especially Weapons) and bring them along in your inventory for the eventual boss fight, but make sure you have non-metallic equipment to use in the dungeon first. Also, don't miss the free Weapons and money in the grass around the outside of the town.