In our house, we generally go for variety in our coffee beans. That means when we are finishing one bag, we’re going to open a different bag with totally different beans inside.
What do you do if there aren’t enough old beans to make a full serving of coffee?
It may be heresey, but I mix the final old beans with a few beans from the new bag and call it my “bonus blend”.
Honestly? I just fill the remaining weight in the grinder with whatever I’ve opened to brew next. Unless the old beans are getting stale, then I just bin the tiny remaining amount.