In New Zealand we have this month made single use plastic bags illegal. So there are a lot less bags going to the oceans from here than previously, which is a good thing. Although there is irony in putting things wrapped in plastic - eg bread, into a non plastic bag and feeling good about myself. A long way to go I guess.
But I think back to my time in Bangkok, where the population is much larger, and they use on average 6 bags a day per person. Watch the video below of the street food vendor, and how many plastic bags they will use for one meal for one person. How does this get solved? These are people with no social welfare, who work nearly every day they have to make money for their family, and often a very very small amount, they are not travelling around the world on holiday. I used to eat street food most days, I got to know many of the people I bought food from reasonably well, they are just normal people trying to get by. I think if they could they would change but the cost differential between a plastic bag and the alternative means they are out of business, work, out of money. And there are huge numbers of these meals served everyday in Bangkok, other parts of Thailand, Cambodia, Vietnam, Laos, all with poor refuse collection, so a very high percentage of the bags are going down the drains and into the rivers and oceans.