Well, I got them all, but it's hard to know which ones you've already done. Some easter eggs that most people miss are:
1) Go to the storage room in the morning at school after you've reached level 1 with Sena
2) At the mall, right side, there's a brown door, you can enter that one.
3) Left side on the mall, black door. It's the anime store scene.
4) At the city park, on the top left is a musical sign, click on that
5) Also at the city park, click on the Sweet Taste sign with the candies on it
6) Jina needs to move in with you, then on Saturdays I think, click on the bottle in her room at noon.
These are the ones I know on top of my head, hope these help you.