For consumption: get a reverse osmosis system. Not eating seafood is an interesting idea, but apparently Omega 3s are so healthy they outweigh the heavy metal exposure, apply that however you want to micro plastics. Don't use plastic dishes or cutlery, don't microwave plastics, don't use plastic ladles, flippers, water bottles, etc.

For not contributing: If your garbage is done properly it's in a landfill. It's the plastic that makes it to the oceans that's bad. It's actually kinda fucked what we can do afaik. Anything that goes into the water is a problem, so any personal products, hygiene products, I wonder about washing synthetic clothes, there's probably better lists out there.