Just want to know what this is
Looks like a heat shield from the muffler. It is there for a reason, have it re-attached or replaced.
Or the outer layer of the muffler. Long hose clamps will probably do the trick for a while anyway.
Do you think I can drive with it for a few days until I can get to a mechanic?
No. It’s a hazard to others when it falls off. Can you wrap a piece of wire around it for now?