There are many things that you can put into your letter bags. I would suggest that you not put too many items inside at one time. You can change out the items to make the bags more interesting. Here are some things that I have used in my bags.
1. Sign Language Flash Cards
I teach my student to use the ASL handsign when learning the letters. I put a flash card of the letter inside the bag for practice.
2. Mini Guided Reading Books - These mini guided reading books are fun to put into the bags. Students can use the pointers or finger puppets to read their books.