I challenged myself to buy no packaged food for a week. I made it 2.5 weeks at zero and the experience improved my life so much I decided to keep going using as little packaging as I comfortably could. As my cooking skills improved I bought more fresh fruits and vegetables and, from bulk bins grains, dried beans, nuts, and dried fruit. I shopped increasingly at farmers markets. I came to see Trader Joe's, Whole Foods, and other markets as wastelands with more garbage than food in them.
I was throwing my trash out once every other week, then once a month. Now the last time I emptied my garbage was September 2018 and the time before that July 2017. Here's a video showing my garbage the first time I went one year without filling a load: http://joshuaspodek.com/year-emptied-garbage.
My food tastes better, costs less, is more convenient, and connects me with my community more, as more people come over and I've visited the farm where most of my vegetables come from.
If you also believe that we need institutional changes from corporations, government, etc, the fastest, most effective way is to start with personal behavior, building on it, and leading others.