If your milk starts to smell not quite right - don't throw it away! You can still use it in recipes.
BAKING
You can still use sour milk for pancakes, muffins, scones, waffles or biscuits. The "off smell" is the rise in acidity and this milk can easily be used instead of buttermilk.
Here is a link to an easy pancake recipe.
If the milk has separated (it "plops" when poured) then toss it, but before then, you can add it to recipes instead of sour cream or yogurt to increase the creamy texture! Your dish will not taste sour.
FREEZE
Yes, you can freeze milk.
If you see the expiration date is approaching and you do not want it to go bad, freeze it for 3 - 6 months! The milk is best within the first month though. Milk will expand when frozen so leave some room in your container. You can leave it in the original plastic container, place it in an airtight container or pour it into ice trays, one cube = 2 TB. You can also use these milk cubes in your next smoothie!
Half and half and cream will also freeze - a perfect addition to your iced coffee instead of ice cubes.
To thaw - place it in the refrigerator overnight. It will have separated slightly, so be sure to shake it up first. Thawing in the refrigerator reduces any bacteria growth.
Taste - the taste of thawed milk will be relatively the same, but you may see a slight difference in texture, a bit grainy. You can fix this by running it through the blender or just use it for recipes instead of a drink!