Regarding the SSM,
As said they are really easily replaced between the Service Manager, Systems Operator and Cashier they can all do most parts of the job (especially if there were 2 cashiers) and a STM or Store Manager can do the management part of the job.
I've done SSM relief and it's easy as, basically you go over everything the cashiers, service managers and systems do. Sales reports, cash balances, wrappings orders, money investigations, check wages with store manager, magazines (order and sort returns) and donations etc, go over all the checkout reports, HR crap and deal with all the shit from Head office that they send you and product recalls and that was pretty much it. Few other things that it involves but really wasn't hard.
Easiest month of my life
Deli and Service manager's jobs are harder! Basically they are a paperwork bitch/bastard.