Sandpaper cards are fantastic for learning letter formation, but lets face it, if you don’t change things up once in a while you (and your children) can get tired of the same ole-same ole.
To make a sensory bag, just put some dish soap or hair gel into the bag. Not too much, you want it to lay fairly flat. Depending on bag size, a few tablespoons should do the trick. If you want to color it, add a bit of food coloring or liquid water colors, then seal up the bag. If you want it to be fairly durable then you might consider duct taping the edges.
You can use the bag by itself having the children write letters from memory or while looking a poster of letters. You can pair the bag with your sandpaper letters by putting a letter under the bag and having the child trace the letter with their finger.
As a side note, LittleMan likes to say the phonetic sounds each letter makes as he traces that letter. This simple act of saying the phonetic sound while not only looking at the letter but also physically tracing the letter really helps him solidify the connection between letter recognition, phonetic sound, and letter formation.by