Zig-zag foot and zipper foot (not pictured): I have other feet, but I don't know what to do with them, and these two fit all my needs.
Tape measure: I always keep it tightly rolled. It bugs me when I'm working with it and all the excess is unrolled and flopping about.
Seam ripper: If I didn't dislike it so much, it would be my best friend. We see alot of each other.
Fabric scissors: In a pinch, I've used my thread scissors, but these are much more comfortable.
Thread scissors: I tried to sharpen these and somehow began to reshape the blades. When one side of the sharpener is marked "left," does that mean you hold that side facing left in your left hand and hold the scissors in your right hand? Or does it mean that you hold that side facing left in your right hand and the scissors are in your left hand? Or do you hold the sharpener in your left hand and point towards your right hand with the scissors whichever side says the name of the kind of scissors you have (left goes out if you have left-handed scissors, right if you have right-handed ones)?
Marking pencils/chalk: I like the pencils better. They work more consistently than chalk, can get a finer point, and the mark doesn't rub off almost immediately.