Here's a recipe for using up your leftover Champagne: combine it with corn syrup and gelatin and make champagne marshmallows.
When you're not feeling especially celebratory, make these with any sparkling wine or even beer (for a whole different animal!). If you'd rather just make a plain ol' marshmallow, check out that recipe here. Leave the vanilla out to let the champagne flavor shine through, or use it to soften the champagne's tartness. If you like the idea of "champagne and roses," whip in a little rose flower water at the end of mixing, with or without the vanilla.