Any first day of school party Ideas?

My niece(4) is starting kindergarten this year and my other niece(7) is going into grade 2. I want to have just a tiny family thing for them but mostly for the younger one, seeing as how it is her first day of school, and need ideas. I was planning on making a cake that looks like a bus and buying those Pillsbury cookies that have buses on them. I also have peel and stick chalkboard paper I'm gonna stick on my table (old table) for scribble fun. I'm thinking yellow,red and a black helium balloon for each and ???? I don't really know of anymore simple ideas. Gonna get pizza for lunch and go to the park. Any good kid friendly movies related to school? Any decorating tips? Need cheap and easy ideas. Thanks!