Anything Simpsons is great - Big Pink Donut, Duff Beer, Flaming Moe, a Squishee from the Quickee Mart. Other than that, Universal isn't quite the culinary delight that other amusement parks are.
I really enjoy most of the offerings at the Simpsons - I had the pink donut last time I went! I also like the Beverly Hills Boulangerie to get a slice of cheesecake.