M.M.
DON'T WORRY!! If you cajole, threaten, bribe him, it will not be worth the effort.
From the list, it seems he has a VERY well balaced diet!! And, he is young.
Don't bribe him with sweets and cola or make food a "big deal." He and his appetite will set limits and needs, and as he grows older, he will add some of the new.
My daughter (now 40) ate only chicken, chocolate milk, apple juice, crackers and peanut butter for YEARS! She is fine, healthy, and smart.
Relax and praise him for eating ANYTHING at that age!!!!