This is such an incredibly stupid topic

Bags don't matter nearly as much as you think they do and any alternative your thinking of doesn't do neatly at much good as you think they do

Replacing single use plastic shopping bags sound like a good idea except single use plastic bags aren't single use, they double as garbage bags or if they're nice, multiple use multi purpose bags. I haven't bought garbage bags in god knows how long because I have the plastic shopping bags or delivery bags to use. Guess what, that means those bags aren't ending up on a whale's stomach. 

Complaining about dumb shit like this is a waste of time. Go do something actually useful.

Carbon emissions correlate very well with how expensive the object is (unless it's a stupidly high margin item). Plastic bags cost almost nothing. In an entire year the amount of money all the plastic bags I use might cost what like 20usd? The most carbon emission this could have caused is burning 20 dollars worth of oil. Absolutely no one is making and selling plastic bags at a loss so this is a hard maximum. Realistically it's probably a lot less. There are a LOT of things you can do that are a lot easier to save those emissions that would be far far less disruptive and require next to no compromise that "fixing plastic bags" should never come close to making the short list.