If I spill something dry on the floor I'll use a dust pan and brush to clean it up. Like this:
But say I don't have one at hand. What standard office supplies can I use the improvise these? I also don't have a vacuum cleaner.
Really would depend for me.
I don't know about the brush, but a piece of paper with one edge wetted with water can do a superior job when brushing up fine powders, because a dust pan will leave a stripe of dust.
A piece of paper or card stock works well as the pan, and a magazine held by the spine, or a bunch of loose papers held together at one end, should work for the brush.