I walk to the park during slow hours, sit on a bench, wait for a bunch of sparrows to come, and then I give them some sunflower seeds. Sometimes -but not often- a magpie will approach too. You
have to be quiet for birds to come near and fairly calm for them to approach you at all.
Others can only be spotted from a distance. Wagtails are quite timid but can be seen running around sometimes, and the blackbirds can be heard a lot even if you don't see them. I've also spotted a couple of woodpeckers. And once the park fell suddenly still and I looked up and there was a kite passing by (they have been spotted nesting in a much larger park a couple of miles away).
If the park is busy, then I'll watch the dogs, people going by. I ponder about the futility of life. Just sit there silently, doing nothing.