Completely random question (bathtub related)

I have a completely random question (sorry if this is the wrong board to ask this on).

I have a very very old bathtub (the kind where the drain control/stopper is outside the bathtub. However, it's not working properly and the bath slowly drains which is irritating. Trying to take a epsom salt baths and constantly have to refill the tub. Anyone have annsiggestions on how to block the drain to prevent this? I know they sell drain blockers but it's a bit too late to go out and get one. Any ideas on a common household item that might work?