One of the ways I engage students on the first day of school is with Play-Doh. I know a lot of teachers (even secondary teachers) use Play-Doh already, including Teach Like a PIRATE Captain Dave Burgess. A chapter in my own book Play Like a PIRATE: Engage Students with Toys, Games, and Comics is about Play-Doh. And you should buy it and read it. Buy ten copies even. One hundred. I won't even be mad.
Specifically for the first day of school, this is what I'd do with Play-Doh: