If go to the city to find out what the hindden Items are do not accept it right away, by not accepting it right away you can try them same item again and you might get something different. Most of the time the items name changes but the affect stays the same but with different power levels.
Example change: fill, drain Example power: often, high chance
When you are fighting the flying bugs and kill them off do not kill the big bug sack, instead warp back to the city then warp back to the field, the back should come back, this should let you have unlimited points to level up your character.
I've only done this twice so I'm not sure how much times you can do this.