when u get to the bikinel desert and u are able to dig for parts u can get attacked by the boss tht u fight in the fifth chapter (cant remeber the name for it though........) if u have theif equipped u can steal mega-elixers from it. which is help full in the early stages to either just use or do what i did and sell them off and buy stuff from the guy in debt on the airship so u can kick him off quicker
. not only do u get the mega-elixers and pay off the guys debt but u can get the parts for the machina too so tht it is more powerful when u get round to fighting it