Mostly no needle at all.
toothpick - expecially on size 0, 1 or 2 needles
safety pin - any type, stitch marker types to sewing types, to stitch holder types (easy to keep attached to the knitting so they don't get lost when not in use)
pen (remove the ink tube)
Really? - A key?? You must have small keys or use large knitting needles!
Fibernut - I'll have to try out your needleless method. I usually switch the stitches around but with my current socks on size 1, I have a hard time getting the dropped stitches back on the needle so it is taking longer then using a holder.