Can of fat-free sweetened, condensed milk
Pour the can of sweetened, condensed milk in a large, clean bottle. Using the empty can, pour the same amount of regular milk into the sweetened milk can and add to the water bottle. Add half of a teaspoon of vanilla extract to the milk, put the lid on your bottle and shake until combined. Continue adding milk until desired sweetness is achieved. Keep refrigerated.
I wouldn't use this in place of a bottle of Coffee Mate, especially when they have their delicious seasonal flavors out, but I would keep a can of the sweetened, condensed milk in my pantry for those annoying times when you've just run out of creamer and don't want to run to the store just to buy some.