When you hover over "Shop", there will be a tab labeled "Rewards". When you click on it it will bring you to a series of text boxes and such. Here, you can gift yourself items and grist. You can also give yourself encounters and Echeladders rungs. Boondollars are included. If you want an item you must select "Item" from the drop down box, choose the amount you want, then, under that, put in the code. This might not be accessible through Challenge Mode.