I probably strip 50-65% of screws that I install. (I know, I'm doing it wrong. For starters, I should step away from my power drill until I learn to be more delicate.) Until I break my bad habits, Mikesaurus's Instructables post "5 Ways to Remove a Stripped Screw" will come in handy. (I've long ago mastered the bonus sixth step: "Leave it.")
This rubber band method is surprisingly effective and doesn't require anything you may not have at home:
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"If the screw isn't totally stripped the rubber band will help fill in the areas where the screw has been stripped and provide friction where it's needed, allowing the screw to be removed."