Wash the celery under the tap and shake off the water. Then cut off the top and lay it on top of the stalks.
Wrap the celery head and tops in aluminium foil so that it is completely covered and sealed in. If you don't want your food touching aluminium, cover it first with a sheet of baking or greaseproof paper.
You can see some of those celery tops above in my leftovers curry we had the other night. I use the leaves more like a herb than a vegetable. You can use them instead of parsley or chives in almost any recipe. They will also make up a delicious pesto, replacing basil leaves with celery leaves. Any stew or soup will be improved with the addition of celery, including the leaves. So don't cut them off and throw them away, if you keep the cut tops in the aluminium parcel with the celery stalks, they be ready to use whenever you need them.