These are pre-sterilized little sacks that slip inside the bottle and hold the breast milk or formula. (pregnancy-info.net)
Click the link and she'll show you how to embroider an inspired statement (like «Yummy») on a piece of canvas and then sew it into a neat little sack that folds down the same way a brown paper sack does, so it won't take up too much room in your purse. (craftstylish.com)
Basically, what burrata looks like is a little sack of soft cheese which is either sealed off or tied off, depending on how it is manufactured. (justalittlebitofbacon.com)