Ok, ok, I know you’re not throwing them out. You’re sauteeing them with garlic and chilli. Or feeding them to the chooks. Or composting them. But you know what I mean.
A 250ml glass jar will hold about one bunch worth of kale stems and take about half a cup of pickling liquid. You’ll have some liquid left over, so throw in any leftover veg you have hanging around at the bottom of the fridge in a similar sized jar. Just about any veg will work.