Illustrations Become Products
If you have created illustrations for your book, are they part of your branding? Can they be made into a sellable product that is low price and an add-on to a sale of a book or stand alone? To do this, you need to get permission of the illustrator or have it arranged up front that you own all rights for anything and everything.
Many will require payment—either a lump sum or royalty arrangement. Judith turned one of the critters in her Stabotage!™ How to Deal with the Pit Bulls, Snakes, Skunks, Scorpions & Slugs in the Health Care Workplace book into a 2 x 3 pin that cost 60 cents that she sells for $5—markets my books whenever it is displayed or worn.