Here are a few recipes from attract wild birds.com
Homemade Suet Cakes
Making homemade suet cakes is simply a matter of melting fat down to a pour-easy consistency, adding a few ingredients of your choosing, then pouring the mixture into a mold. The shape of the mold is determined by the type of suet feeder you'll use.
If you are using lard or shortening for homemade suet cakes, adding equal parts of peanut butter flour will help maintain correct consistency of regular suet cakes.
To this warm and pour-able mixture you could add rolled oats, bird seed, cornmeal, raisins, unsalted nuts and anything else you think the birds would enjoy. Then, pour your warm suet 'soup' into the mold (a bread pan where you could slice off bits for your store bought suet feeder, cupcake tins that you could pierce with wire and hang from a tree, etc.) Specialty recipes are at the bottom of this page.
Keep any unused portions in the freezer for up to two months.