S.H.
There are a lot of ideas already. I am a big fan of sneaking in vegies. My son is also more willing to eat anything as long as there is dip, so I use everything from BBQ sause, honey, Ranch, Tahini, Humus, etc with each meal.
But I just wanted to tell you not forget snacks. I am a big fan of raisins, banana chips, dried fruit, soy beans, nuts, cereal & fiber bars. And my son eats and asks for these things. Also I buy the juice with fruit and vegetable servings like V8 fusion and the Fresh & Easy version.