There are so many ideas I do, but I can't say that I made them all up myself. I've altered some of them so I guess that's partially creating some.
Here are some of my favorites (and the kids' favorites!):
1. Open House - "Treasure Hunt" - Give the kids a list of things to show their parents in the room (class pet, their desk, etc...). The last thing on there is for them to find the treasure chest and it has a goody bag for each child (a few small things in it - piece of candy, pencil, eraser, homework pass, etc...).
2. First Day - Read Chysanthemum. I've posted about this before, so I'll give a shortened version. As you're reading the book, when the mouse gets insulted make a tear in a paper doll. When she gets complimented, put tape over the tear. In the end, explain how words can hurt feelings and you're better after encouragement but not ever quite the same. I keep the doll taped near the white board as a reminder all year about talking nice to others.
3. People Bingo - I have a grid with 25 spaces on it. Each one has different items on it (someone with earrings, born in another state, etc...). The kids walk around the room and find someone different for each square - then he/she signs it. You can end it when someone gets a regular Bingo (5 in a row in any direction) or a complete "blackout".
4. Time Capsule - I take a picture on the first day of each child. They fill out a form that has their shoe size, date, shirt size, height, tracing of their hand, and a drawn picture of them. They put the form along with the picture taped/glued to it in a papertowel tube and close the ends with cupcake liners and rubber bands. They can decorate the outside with their name and stickers. I hide those in a cabinet and let them take them home at the end of the year, after they do a 2nd one (on the back) to show how much they've changed through the year!