Find out the name of that book that he's been looking for.
See if they have it at a used book store.
Of course, you'll have to pay in cash since anything you debit, he'll see! He does such a good job budgeting and keeping an eye on everything that goes in and out of the bank accounts.
If you don't have any cash on hand, you can break into the change buckets, hoping he doesn't keep too close of an eye on those!
You can also make an attempt at your first cheesecake since it's his favorite.
You can always count on the fact that your family won't pass up an opportunity to treat him (and you) to Superdawg!
And you can also be thankful that his family threw him a birthday party.