Burgers are great, too. Have you tried just a basic burger, or have you tried anything more out there like one with cheese and bacon or avocado or onion rings? Have you tried onion rings?
I'd be happy to make a list for you! Do you have any sorts of general flavor preferences or flavors to avoid? A knish is kind of like bread (more like a pastry, like a bun) filled with meat or potato or just about anything really. So basically just something (say, meat, though you can do just about anything) that gets wrapped in the bread/bun/pastry, and then it's baked, fried, or grilled, and they can be small or large depending on who makes it. You can't be in New York and not eat a knish or five.