I love the scatterogies idea! I am in my 2nd year of teaching 7th grade now (well just teaching in general), and I am starting out with lesson 1 just because my new group of kids were out of control in 6th grade, so I am setting the rules up quickly. But I want to use it for a review game or CST review!
As for fun first day activities, you could also try having them do a math art activity like positive and negative drawings/colorings/paintings using 2D figures - and then either link this to positive and negative numbers (that is my first chapter), or a refresher on the different types of shapes/figures. And then you would even have something to put up!