My 2.5 yr. old's food "choices" need to change. Is it ok to let him refuse the new stuff for a day or so?

Good ol' grampa loves to sneak him chicken nuggets SEVERAL times a week while I'm at work and my husband doesn't seem to mind. He thinks it's cute. Now my son only wants to eat 2-3 specific things and turns his nose up to everything else. I end up giving in because I don't want him to be hungry. He's at a healthy weight so I figure if I'm headstrong about only giving him organic healthy foods, eventually he'll get hungry enough and eat whatever I serve him...Right? Help! He's my first child so I'm trying to learn all this stuff...