My wife has been using this wine saver vacuum pump for several years now. It creates an airtight vacuum in the bottle to preserve the wine.
The pump comes with two rubber stoppers with one-way valves. You insert the stopper into a partially full wine bottle, then suck the air out with the pump. It looks like a little bike pump. After several strokes, you'll hear a "click," which means you've drawn out as much air as you're going to be able to remove. At $8.50 am Amazon, it's paid for itself many times over.
The fact that I am considered an adult is both terrifying and hillarious