The illustrator can bring the materials themselves, or you can arrange that. It can be fun if everyone gets a set of markers and a notebook to keep after the session to they can keep using their visual skills. Notebooks branded with your company logo are often a nice touch. It’s a good idea to discuss this before the workshop.
The drawing workshop can also take place online! In that case, the illustrator will communicate in advance what it takes for everyone to participate properly from home.