It says I need to fill in the "Cost or adjusted basis in the donated property" for my donations. What do I put in there?

Why would the cost (or "basis") of an item get adjusted?

Perhaps you used the item in a business setting and depreciated it before donating it. Each dollar of depreciation is subtracted from the original cost or basis, hence, the basis is "adjusted".

If you made substantial improvements to the item before you donated it (as opposed to repairs and maintenance), then you increase the basis by adding the cost of the improvement to the original cost. Example: you added a new bathroom to a house before donating it to a qualified charity.

As noted, normal wear and tear on personal use items and normal repairs and maintenance do not adjust the basis, so for many donated items, the cost and the adjusted basis are the same.

If it is asking for the cost, include the amount you paid for the items.

If it is asking for Fair Market Value, please see this Value Guide.