The staff planner module lets you manage who works where and when. You can set 'demand', by configuring what you need, and then you can plan your workforce accordingly. Catermonkey will give a warning when an event is under-staffed compared to your demand predictions.
Inviting and planning
You can specify the workforce you need, and then invite your staff to come to work, or plan them in directly. It can make an automatic selection based on the skills you attribute to your team members.
Personal roster page for your staff
Your staff all get a (free) login to their personal page, where they can see their roster, and where they can RSVP to invitations. Also, reminders are sent via e-mail.