Surely you could make a far greater environment impact by donating $50 to a conservation or carbon credit charity instead of spending $100 on $50 worth of groceries that have less plastic in their supply chain.
The cost of diverting plastic from the waste stream is high, the cost of recovering it once it becomes litter is higher, and the cost of getting it out of the ocean is dollars per kilogramme. And once we have it the best option we have is either melting into lumps of generic plastic to use as weights, or shipping it to Sweden to be burned to generate electricity (only place that does this AFAIK, and I wouldn't trust anyone in the US or Australia if they wanted to).