Resist the urge to snip the snag or you may end up with a hole in the garment. First try stretching the fabric gently to see if the snag pulls itself back into place. If not, push the snag to the wrong side of the fabric with the blunt end of a needle, then make a knot with the snag. If it’s too short, dab the end with clear nail polish, being careful not to stain the fabric.
If your sewing kit is…well, nonexistent, consult this list of basic sewing kit essentials before stocking up.