Enter Barren Earth, the fourth Earth Forest. When you get inside, at many of the Ogre Vines there will be either a Cute Gem or a Lovely Gem which you can sell for good money.
Collect Inferno Books and Twill Mugworts from the Fire Tower Forest and buy some Luch Eggs five is best from the Kikinak Company. Then, enter the Wind Patina Forest and take a left to the second Ogre Vine. Inside is a plant that merges items. Place the Luch Egg inside, and then place the Inferno Book or the Twill Mugwort in. Do not place them in the reversed order or you will not get anything good. You have a good chance of getting a rare egg with this method.