Here is an opportunity to utilize your current (probably large!) stock of formula tins as toys for your baby.
Using an empty formula tin, put in a handful of marbles, acorns, pebbles, or small stones, anything can be used that will make a strong noise against the metal of the tin. Secure the lid on tightly using tape the whole way around the lid and tin. Cover the whole tin with bright wrapping paper or contact (sticky backed) paper. A baby learning to crawl can rattle these around the floor.
Making a set of these is great fun and as baby gets older the way they play with them will change. Try changing the paper on the outside regularly to provide a different stimulating design, and change the contents as well to allow for baby to hear new sounds.