Some people save the seeds from squash and melons. These are relished by many bird species, sometimes more than black oil sunflower. They should be spread out on trays and air dried before they're placed in feeders, and if dried sufficiently, can be saved all summer for use the next winter. Smaller birds may have a tough time breaking open vegetable seeds, but if they are chopped up with a food processor, most birds can eat them with ease. Other seeds attractive to birds include safflower, the food of choice for cardinals, and peanuts, which are eaten by all birds except for woodpeckers.
Some folks throw out scraps of stale bread, cake, or doughnuts for their feathered visitors.
There's probably nothing wrong with this, but be sure the foods are not moldy, or they may be harmful to birds. Whatever seed you decide to provide, be sure to store it in tight, waterproof containers. Metal containers will prevent rodents from gnawing their way into your food supply. Providing Suet Suet, an animal fat, is attractive to many insect-eating birds such as chickadees, woodpeckers, and nuthatches. Suet is strictly a wintertime food, as it turns rancid when temperatures rise above 70 degrees Fahrenheit.