Buttermilk pops up in many recipes for muffins, quick breads (such as pumpkin and other breads of that ilk), and pancakes.
Don’t skip the buttermilk. It adds lightness to the batter and even in a small amount is likely essential to the recipe.
Don’t buy buttermilk. There’s nothing else to really use it for and it is likely to spoil before you use it up.
Do make your own! Take any regular milk from your fridge and add a bit of fresh squeezed lemon juice or apple cider vinegar (use the ratio of 1 teaspoon of the acid for every 1 cup of milk). Voila – homemade buttermilk!
p.s. Try one of my favorite fall recipes (which includes buttermilk): Macrina Bakery Pumpkin Bread