> 75% of the time I forget to take a bag to my car.

Then take a bunch in the other 25%. You can just leave them in the car.

Grab a bundle right now, or whenever you’re at home and remember, and put them next to your keys, your wallet, or hang them on the handle of your door.

> I like them better as they are bigger and stronger.

Sure, use whatever you like. Just don’t let perfect be in the way of good.

> Even if I managed to get a bag, the other 75% of the time I forget to take it into the shop and leave it in my car.

Then go back to your car! It will be mildly annoying the first two times, and the third time it won’t happen. I mentioned exactly that in my comment.

> Even if I manage all of that, 25% of the time I will end up not having enough bags.

Then start bringing more. This isn’t hard. Leave the extras in your car.

Or just use the cardboard box approach I mentioned.

None of your mentioned obstacles is insurmountable. On the contrary, they are all exceedingly trivial to overcome with the tiniest amount of will to do so.