Panicking? I have been.
This resource has 2 simple first day activities.
One worksheet is a 'find someone who' double sided questionnaire...students can circulate around the room and try to find a classmate who has or can x,y,z and write the name in the box. (you may need to edit some of the questions for your school and grade)
Other worksheet (Getting to know you)I may put on the tables when students arrive and they can fill in the answers about themselves and their interests, strengths and weaknesses.
Hope they help new classes.