Birds love suet in the winter. The most common type is animal fat. You can buy this from your butcher. If you chose this method, first cut the fat into small pieces, removing all meat. Next, heat the fat on low heat until liquified. If you heat it on high, you risk starting a fire, or scorching the fat. Once liquified, strain the fat through cheesecloth. Repeat the straining to remove all small particles. If you saved old trays, you can pour the melted fat into these molds to make your suet, if not, a sandwich sized Tupperware or Rubbermaid container works well. You can roll this rendered suet bird seed or nuts.
Another option is when the suet is liquifed, add an equal amount of chunky peanut butter, corn meal, and wheat or white flour. Melt the fat and peanut butter together, then add the flour and corn meal, then pour into your molds. Refrigerate or freeze until you are ready to use.
You can also add dried fruit bits, unsalted nuts, bird seed or meal worms. This mixture can also be rubbed on and into pine cones to make winter decorations for the birds in your backyard.
For non-melting suet, save old suet packages or sandwich-sized plastic containers work well. Fill them with nuts, mealworms or dried fruit bits. Next mix gelitin to the package instructions, and dump on top of your mixture. Let it cool, then wrap tightly and store until you are ready to use them. If you don't wrap them, they could attract pests like mice and insects.