If you are looking for a useful addition to your artist tool kit, then consider a water brush. A gadget which fits into your pencil case, carrying a water brush means you do not have to have a clutter of jam jars, brushes or fiddly little bottles when you are out drawing in the landscape, making studies in a museum, or quick portraits in a cafe.
A bit like a fountain pen with water instead of ink, the synthetic brush tip enables you to apply a wash to watercolour crayon or water-soluble graphite, and the refillable reservoir holds a surprising quantity of water.