To recieve extra items for your campaign talk to Feydwer and Klaars when you are in Seahaven and tell them you have a code for them. These items each require a 'Master Code' and 'Content Code' and when entered you'll recieve the corresponding item.

Master Code:
Enter MPJNKBHAKANLPGHD

Unlock Bloodstained Warboots:
Enter MHFMCJIFNDHOKLPM

Teasha's Ire (Katana):
Enter GDIMBNLEIGNNLOEG

Enkindled Cleaver:
Enter MJPOBGFNLKELLLLP

Malignant Force (Bow):
Enter JDGJHKPOLNMCGHNC

Polychromatic Shiv:
Enter PJJEPCFHEIHAJEEE

Unlock Bolt Flingers (Gloves):
Enter OBMIDNBJNPFKADCL

Traveler's Handbook (Trinket):
Enter PIJNPEGFJJPFALNO

Unlock Elite Mode:
Successfully beat the game once to unlock Elite mode. This mode has the same story and enemies except at 50 levels higher then the first time through.

Get Free Items from Klars
Enter the code 'OGIAOLGCDMOEHLHA' without the quotes to talk to Klars in Seahavenand and get free items.