Writing in salt (this site has Montessori & Montessori-inspired activities).
Set up a simple fine motor activity to work on letter recognition. This letter matching activity can be set up various ways depending on your child's skill level: alphabetical order, uppercase/ lowercase letter recognition, sequencing, etc!
Playdough Letter Tracing ... for letter recognition and fine motor.
Tons of free ESL/ELD flashcards! The clip art would also be useful for regular language arts vocabulary lessons.