Free items
Save the game before you buy the item that you want, then buy it. Make sure you have enough Gald for it. After you buy it, go to the inn. Talk to the innkeeper and select "Trade" from the list of options. Make sure your friend does the same. Then trade your friend the thing you just bought for a worthless item. After the trade, reload the game from the previous save point before the purchase. Your money will be the same as before you bought the item. Go back to the inn and trade your friend a worthless item for the item that was just traded. You will now have the item but will not have spend any Gald.
Magic Knight Invitation
Once you are about level 40, check with Raine in the Ailily guild until you find a quest from Kratos requesting you to battle him. He is not easy to defeat, with close to 30,000 HP and a near instant heal that he uses whenever his health gets low. When you defeat him he will say that he is amazed that you surpassed him, and will give you the Magic Knight Invitation. This allows you to change your class to Magic Knight. You will need 1,000 grade before you can change to this class.
Neverending Search Point
Head to the Foot of the World Tree and stay on the first level. Go to the intersection here, and go to the left. Head around the corner and go past the widened area. Then, when the path narrows, go to the first search point. Use any sickle, and no matter how many times you use them, the search point will mysteriously never wear out.
New Game+
After completing the game you have the option of starting a new one with your current status and items in possesion.
Ninja Invitation
To get a Ninja invitation, you first need to have a level 30+ fighter. After reaching level 30+, keep doing quests in Gavada to build up fame until the "Test your skills with Senel" quest is available. Take this quest and defeat Senel. Note: It is nearly impossible to defeat Senel at level 30. Train your fighter to level 35 or higher before fighting Senel. After defeating Senel, report back to him. You will be rewarded for the quest. Afterwards, talk to him again. Senel will give you the Ninja Invitation. Note: It takes 1000 grade points to change to Ninja.
Start with 900+ LUK
When creating a character at the start, leave the default name of "Player" and you will start with 900+ LUK.