Her First Day of School is great! She provides a plan and some wonderful activities! And....it's written for middle school, which is so hard to find!
Back to school: Read about what you can do in the first five days of the school year (specifically middle school science)
Playing Yahtzee in Lunch Bunch with a special score sheet to use as an icebreaker!
I "mustache" you a question. . . fun game for Lunch Bunch.
Geocaching - a bit late for getting to know yous, but a great team building, get moving activity to use for other content
Adaptation for middle school- use as whole class activity at the beginning of a public speaking unit. Good way to teach the "talk about what you know" concept.