I'm using sage as an example here because it's never around when you want it (like when I made my Christmas Dinner Pies) and my stash of frozen sage saved me from certain doom. And of course, three days later, the supermarket was full of little packs of fresh sage leaves. So I bought some and froze it, knowing that I'll have plenty to keep me going.
Freezing sage is easy : pick the leaves from the stem and check them carefully to make sure there's no brown bits - throw those leaves away. Give them a quick pat with a piece of kitchen paper and pack them flat into a ziplock bag before putting them into your freezer. I actually have two freezers, a huge fridge freezer in the kitchen and a chest freezer in the SuperShed, both crammed to the brim with food.
You can freeze loads of other types of herbs too. I regularly snip chives into a container and reduce great big bunches of flat leaf parsley to smithereens, both of which reside in my freezer and defrost in seconds when I need them. Thyme freezes best when you strip the leaves from the stem rather than freezing the woody stems, and the same goes for rosemary.
All it takes is 10 short minutes and you're sorted. Now you can sit down and relax...