This glass jar should not be missing on your workbench. while working you can, for example, store your clay in it, but also as a water dish or even temporarily store homemade pasta. The paste will eventually dry up, but can be made workable again quickly with a little moisture. The lid prevents quick drying out and keeps your paste or water free of dust.
Make sure to store the clay in an airtight environment after working so that it remains flexible.