We put out a large scoop of whole kernel corn every evening. It's meant for the deer, but the squirrels and birds (usually blue jays and starlings) nab their share.
My Dad put up an expensive, prefab bird feeder years ago, but the squirrels kept raiding and damaging it. He came up with a clever solution, he spread a coating of thick aircraft maintenance grease over the entire length of the pole. It was like watching a cartoon, the squirrels leaping onto the pole, then sliding down slowly, clawing all the way down. The funniest part was watching the squirrels rolling around and scooting across the grass trying to get the grease off them.