One might count these as tips, but they are the “I’m really too lazy” versions of those.
I don’t use that much buttermilk. On the rare occasion I use it, it’s for a recipe that calls for one cup. At most. But you can only get it in quart size. What am I going to do with the remaining 3 cups? Well the reason most of those recipes call for buttermilk is the acidic components (high levels of lactic acid) and low fat content. It is used often in baking because the acid reacts with baking soda to create bubbles in the batter as it is cooking.
The quick and easy replication of the same effects is to add ~1 tbsp lemon juice – or even white vinegar – to 1 cup of milk (a tip I picked up from Smitten Kitchen years ago). The milk will curdle a bit, but in this case, that’s just fine. You’re not drinking it straight. It will do its job in the recipe without having to purchase anything you don’t already have in the house. On the other hand, there are times you want the full flavor of real buttermilk (i.e. buttermilk ice cream), so don’t skip it then, this won’t taste the same on its own.