Voluntary service unto others is a great boon to any society, either mundanely or within a recreation group. It is part of what keeps any group cohesive, running well and helps everyone have fun.
In the SCA, this could be staying back and helping after a feast to clean up, autocratting, feastocratting, teaching people new skills, assisting people with their projects, helping newbies, writing and revising SCA paperwork e.g. marshal's handbook, holding an office (and fulfilling its role), and simply enriching the Society with support and generosity.
The SCA has various awards for good service. These range from the local level (e.g. Baronial level awards) to Kingdom level awards. People who have excelled in service are elevated to the Order of the Pelican which is recognised through the Society.