Sometimes you can't finish a bottle of wine but you don't want to toss out the remaining amount. To preserve it longer, you need a good wine stopper or other tools. If one isn't to hand, consider using a smaller container.
Photo by Kelly Teague
Redditor Axel927 suggests that approach:
Honestly your best bet is to finish the wine. The reason the wine goes bad is contact with air, so here's what I recommend: Pour the leftover wine into a smaller container - if the wine takes up most of the container volume, then there will be less room for air. A mason or canning jar works great. Make sure the seal is airtight. Keep it in something that is 70 degrees F or cooler.
If you don't want to spend any money, this is not a bad way to make sure that wine doesn't go to waste.