There was an Old Lady who Swallowed a Fly was one of my favorite books to read in Elementary School. It is such a fun book, and I love that there is a song you can use to follow along with. There are so many fun activities that you can use this book for.
I would use this book in kindergarten or first grade, and one thing you can do that I did in a class is cut out small pictures of each animal in the story, separating your students into groups for an activity. You can also use a paper plate to make an old lady, the plate being her stomach, and cut out pictures of each animal that she eats and gluing it to the plate; you can have your students color it and hang it up.
Another thing you can do is an sequencing activity sheet, cutting out the animals and gluing them to a paper in the order they were eaten.