Both clubs have a similar number of sites and site staff, so I am assuming my answer covers the C&MC as well as C&CC.
Head office staff are as vital to the smooth running of the clubs, as site staff. So in no particular order!
Departments include Customer Services and call centre staff. Operational Site Support Staff, ( to order new site equipment, including machinery, site shops and other practical help for site staff. An accounts dept to pay bills for sites and head office and control on site spending etc. Property and Development department for building and existing site maintenance and repairs and finding and developing new sites. A H&S and staff training department. Membership Services to look after member queries and membership renewal queries. Senior management to plan and run the show. Regional managers to support site managers and staff at local level. IT department to look after the IT stuff. HR to make sure sites are staffed, employment laws are followed and site staff get their pay and conditions looked after. Club marketing dept, who make sure members are kept up to date with offers and information, and put together the club magazine. There maybe other that I have forgotten to mention, but believe me they are ALL required to keep an organisation, each with 115-120 club sites and over 1000 CL/CS up and functioning for the members and customers.