Learn English – this thing that you put a sword in called

In my experience, which is all I can answer from, in American English, 99% of the time the white plastic object is called a bag.

Specifically, it is a plastic bag.

We also have paper bags. And canvas bags.

When you start talking about "bags" made out of thicker material, traditionally woven from cotton or something, you can then use the word sack.

You can use sack to refer to a paper bag, but it is rare to refer to a plastic bag as a plastic sack, in the USA, using American English, at least in the dialect I speak.

So, in short, yes, bag is the most common term to call the white plastic object.

As FumbleFingers said in a comment:

Some people might call it a decal (2. A decorative sticker) Amazon sells them as decal stickers.

My immediate thought (even before seeing the image) was "decal".

"Sticker" is a great word and it is perfectly accurate but "decal" (Google Image search) has the added meaning (in my head, at least) of being a simple image, often a logo.