As others have said, most people store their stuff on or under the footrest, so you'll sometimes see stuff rolling backwards during takeoff. If you do decide to put anything there, just be sure to hold it in place with your foot.
There's also a little storage area right under the screen. Not exactly sure what it was originally designed for, but it will fit a laptop and a few other thing - I usually put my laptop there, and haven't had any issues with it falling out during takeoff.

FYI, row 1 middle bulkhead seats on the 787 lack any overhead storage.