Pack lunches in a stainless steel or glass box with compartments, add a steel bottle and cutlery from home, and skip individually wrapped snacks.
A daily packed lunch in cling film, a zip bag and a snack packet is roughly 10 g of plastic; 200 school or work days is about 2 kg a year. A reusable box only pays off after many uses, and eliminating and reusing sit at the top of the Ellen MacArthur Foundation's upstream-innovation hierarchy.
The catch: steel boxes are heavy and pricey and cannot go in the microwave; a durable PP box you already own is a fine substitute.