Is it OK to stuff steel wool in an outlet ? Mine is loose fitting and I don't want mice sneaking in,

Steel wool is a conductor, so at the least you'd trip the breaker, at the worst you could start a fire or get yourself electrocuted.
Bottom line, DON'T DO IT!

Use Tough Stuff. It is a foam insulation. Read directions.

Chuck

There is no way this question is for real. Please tell me it's not for real.

Tighten all the yoke screws. If they are stripped, drill and tap for 8-32.

Seal all un-used KO's with push-pennies, and install cover plates.

Nah... I think you should paint it yellow...