Writing in salt (this site has Montessori & Montessori-inspired activities). Really need to start doing this!!! Practice Letters, Montessori Activities, Practice Writing, Salts Writing, Montessori Inspiration, Letters Writing, Writing Letters, Shaving Cream, Learning Letters
Also on these boards
how to make colored salt - great for sensory play, and in a writing tray for sensory learning
Q-tip Painting to practice writing letters...and numbers. I'd photocopy the Handwriting Without Tears book and their alphabet if that's the writing program used in your school district or whatever program they use if they use one in yours so you can directly connect the two to administration.
Helpful sequence and guidelines for introducing letters to children via Lessons Learnt Journal.