Ever since I bought my car and begin grocery shopping on my own, I've tried to avoid using plastic bags. Instead, I use regular reusable shopping bags like these or a cardboard box (I have a few of these at home). The former cost 1 USD each and don't break or tear as easily as disposable plastic bags.
One practical reason why I do not use plastic bags is because they tear easily. Some people use them for a garbage disposal but I don't because they usually have holes in them. A stray chicken bone or prawn shell can easily pierce the flimsy plastic material. Once a hole is made in the bag, rubbish can leak into the bin and dirty it. Hence, it is a better idea to use regular garbage bags.
Another reason is that I usually get more plastic bags than I need. After a trip to the local grocery place, I get about ten plastic bags, sometimes more. That's really more than I need even if I were to use them for garbage disposal. Before I stopped using plastic bags, I would save the plastic bags I got from my grocery shopping. Within half a year, I accumulated a whole box full of bags that I could not use up. Furthermore, many of them had holes in them and could not be used for garbage disposal. In the end, I had to bring them to the plastic bag recycling bin at the grocer's. I'm sure many people simply throw away their excess plastic bags.
What finally led me to use reusable shopping bags was when I read about the Great Pacific Garbage Patch. Because plastic bags tear so easily, pieces of them are blown from landfills, which don't have to be near the sea, and accumulate in the oceans. The plastic remain in polymer form and after they are broken down into small enough pieces, they enter the food chain. I don't have to tell you what a bad idea it is to have fish nibbling or seabirds choking on small pieces of plastic.
It is not difficult to switch to using reusable shopping bags. They are actually convenient (since they are more durable), make housekeeping easier (less clutter) and reduce the amount of plastic that goes into our seafood.
Please make the switch.