Train Initial Sound Sort
I'm working on initial sounds of words with one of my students, so I made this sorting activity to practice the concept. The first version of the activity is just to sort the matching letters into the correct cars on the train, just to get the student used to how the sorting activity works.
Once the student has mastered this, we moved onto the sorting by initial sounds. You can get the printable activities here (the file is editable, so you can change the letters and pictures after you've done these): http://www.positivelyautism.com/downloads/trainlettersort.pptx
Note: some of the pre-reading activities that I recommend doing before working on activities like this (and phonics instruction) are found in this book:
Another book I like with activities for teaching reading is this one. I think a lot of these activities can be easily adapted for students with autism.