How can I save money on food?

I'm new to couponing. but there's a problem. I see on youtube the people that get $300 worth of groceries for like $20 never buy anything nutritious. (like 20 bottles of coke for $5, come on... seriously?) I eat boneless, skinless chicken, ground turkey, multigrain bread, and lots of fruits and veggies. How can I save money on healthy food i buy?