Back to school idea - "We're looking back on summer, this is what we see!" Have students draw pictures of things they have done over summer break in sunglasses. You could also do it for things students are looking forward to this year.
All about me bag - Each child fills the bag with 4 things about them and brings it into school. They can decorate the bag too. I did this with my own items as a first day of school ice breaker. Maybe get large paper sacks from the grocery
"Check Out the Lineup in." Using a T-shirt theme and hanging student shirts along a clothing line is a colorful idea for a Back To School bulletin board display. You can also have the children decorate their t-shirt