For cats veggies are not really advisable, they can't break down vegetable food properly. My little Alt likes chewing on grass when I take him out for a walk, but that is because it helps him clean his stomach. Ever since he does I've never seen him coughing up a hairball, so in his case grass is probably working!
He is really a weird cat when it comes to food. He doesn't like ham, chicken, salami, and many other things that would be delightful to any other cat. He only eats wet cat food from two brands, any other brand and he'll scratch the ground to signal his dislike. But he likes potatoes and croissants!
I noticed that he is more willing to try unorthodox food when he sees me eating it. For example, if I'm eating bread and I give him a small piece of it he will eat it gladly, but if I leave it in his bowl he won't touch it!