Whenever I go grocery shopping I always make sure to bring my own reusable bag to help save plastic. I have a couple: some basic ones, some with a cute print. But nothing quite as adorable as this Japanese mouse.
It is beautiful when zipped up, but also unfolds into a really cute green tote with a lovely print. And even then you can still see the mouse, because it sticks to the side of the bag. Which also means you will never lose the pouch.
It is a bit pricey, but I imagine it would last a very long time too. Anyway, you can get one at Japanistic.