Here is an idea for some preschoolers:

When my DD6 was in preschool her brother was in 1st Grade. She felt bad because he was going to school 5 days and she only had the option of 3 half days. We decided to home school the other 2 days. We got a journal with the goal in mind to list and do 3 activities that were learning. She was practicing her writing and spelling with the activity list. She also did drawings to make the book fun. It was a very flexible plan. We could spend the day with a playmate or at a nature class or with a list like bake cookies, paint and walk with Mom. We now have a wonderful keepsake from this time. She was very proud of this. People would ask are you in preschool? She would say yes and Mom home schools me the other two days.