In Japan major supermarket chains now give you a discount if you choose to refuse a bag, but it's on the order of 2 yen, and it's an "opt-out" thing rather than an opt-in thing.
In SA, you pay for any plastic bag that is bought at a supermarket or similar store. If it contains a product which is not perishable (like clothes), then you usually get a different type of paper or plastic bag with it without charge.
I think I said this in a funny way, because this slightly differs from store to storeāI am not sure whether the regulations are applied uniformly. (Takeaways, for instance.) But yes, if it is perishable, then usually you pay for the bag.