that box is your pcm (cars computer)
alot of guys just leave it laying there and say its fine, but i wouldnt do this, in my mind its to crucial of a component to be lef laying around.
some guys have used zip ties to hold it in place. I believe i heard that chevy s10s have a tray for it that is a perfect match for our cars, you could probably find one at a junkyard for cheap.