Picky about food

My son is always picky about what he will eat I can not take him anywhere to buy him foods. When he was just a little baby I would feed him every thing I was eating mostly Pilipino foods but when he got a little older he started to get picky and we do not know why. When we go to a restaurant all he wants to eat are fries and fried chicken and when he is at home all he eats is chicken from Walmart if it is from Kroger or other brand he will not eat them. He will also eat rice with soup that I make for him. He will eat apples, cereals without milk, and his second most favorite food other than chicken is either grapes or waffles. Just lately he told me that he is tired of eating chicken now and he wanted to eat other foods. I do not know what kind of foods because if I asked him to try something he says no, so I do not know what he wants hopefully he will start eating other foods soon.