2lbs 7.2 oz
A liter of vodka weighs approximately 2.2 pounds.
I assume you mean what's the weight in ounces of a volumetric ounce of vodka. One liter of vodka (33.814 volumetric oz) weighs 33.404 ounces, so one liquid ounce of vodka would weigh .98787 ounces. That's for vodka that's 40% alcohol - the number might be slightly different for different proofs.
a liter bottle, or two half liter bottles
It depends on that specific bottle. There is no standard weight.
An empty plastic 2 liter pop bottle typically weighs around 40-50 grams.
A liter of water weighs approximately 2.2 pounds. So a 1.00 liter bottle of drinking water would weigh about 2.2 pounds.
A 2 liter bottle of soda typically weighs around 4.4 pounds when it is filled with liquid.
I think a 2-liter bottle of soda, assuming moderate density (such as mountain dew or dr. pepper) generally weighs near 1500-1600 grams.
A full 2 liter bottle of soft drink should weigh around 2000 grams.
Air
As the amount of ounces per liter is 33.824 and 750ml is 33.824 x .75, then the ounces per 750ml bottle would equal 25.368 oz. Using the standard 5 oz glass, there are about 5 glasses per bottle of wine.