This method of letter sound recognition has been working very well for my five-year-old. Using stickers of random pictures, little erasers with pictures on them, and other little trinkets we find either at home or the dollar store, he says the word and determines which tray to place the item in.
If your child is like mine, he never wants to throw ANYTHING away. This works well for those little trinkets you want to get rid of, but they just don't have the heart to part with. They can store their treasures in the corresponding letter drawers.