I made a visit to my local walmart and Sam's club to see how much plastic bags they use. Walmart give plastic bags for free for anything you buy, you can go and buy a bar of chocolate and they give it to you with a plastic bag, different from Sam's club, that they charge you extra if you want plastic bags, if you want your products in bags they charge you $1 MXN (Like $0,054 USD).
Asking people leaving Sam's club about why they didn't use any plastic bags they told me that "They didn't really need them".
When they ask for a bag to put their groceries on the store staff responds that it would cost $1 extra, that moment the customers evaluates if it's really necessary. It's something similar to what Psychiatrist Judson Brewer says about bad habits, if you just take a moment to really understand if you need a plastic bag, you can see you don't really need it to get to your car.