Try making some homemade breads such as banana bread, or veggie breads. You can puree veggies or fruit (various squash, peas, sweet potatoes) and add it to the bread or even use baby jarred foods. Every time you feed him, always make fruits and veggies a choice. Don't get upset when he does not eat them but make sure they are there in small amounts. Encourage him to eat them with rewards. If he TRIES it he gets this reward (something he enjoys eating or doing) and if he eats it all he gets an upgraded version of the reward. For example, take away the soda completely for a week or so. Water is the BEST thing in the world for him to drink so don't fret. Then, after a week or two, use soda as an offering for him eating different foods. If he TRIES the food (he can spit it out in a napkin or the trash if he doesn't like it) he can have half a glass of soda with dinner. But if he eats it ALL, then he gets a full glass. If he refuses just say, "Okay it's fine. Maybe next time!"

Milk is actually terrible for us! The entire it gives us calcium thing is a total lie. We LOSE calcium in our bones every time we consume milk because cows milk makes our blood acidic and our body will draw from our bones to flush the acidity from our blood! :)

At 7, you can really get him into helping with meal prep and cooking even if it is just small things. Of course this depends on the child and his abilities... but kids as young as 2 can be kitchen helpers with meal prep - so find a way to include him when you prepare meals at least 3 times a week... more if you can/he is willing. It works great for many kids (but not all) and it's totally worth a shot. If he participates in helping make the food, he may be more willing to try it/eat it.

We started a food program with our ABA therapist. We started rewarding with 30 seconds of iPad when he would touch new food to his lips, a minute when he would take a bite and not spit it out. We were very careful to say "thanks for trying" in a nonchalant tone when we weren't successful but celebrate when bites were made.
Oftentimes I purée food and add it to sauces or batters. My son loves pancakes and waffles so I add chia seeds and he likes Alfredo so when I make it at home I purée a can of white beans and it for extra fiber and protein, etc....
Good luck! It's tough when the little ones won't eat.

I have a lot of trouble getting both of my boys 12 and 8 to eat a variety of foods too. You could try Silk Vanilla soy milk, my 8 year old likes this brand only. Try giving small rewards for trying new foods. Maybe get him checked for food allergies, both of my boys have them.

Tried that too with the smoothies. My son has VERY SENSITIVE taste buds. That is why all of his foods have to be fixed exactly the same every time or he won't eat it. I have had to throw away a lot of food.

I hide food in vegetable and fruit smoothies with unsweetened coconut water as a base.