Anything that may be done by both volunteers and professionals:
1) Religious activities (not all of them, but quite a lot)
2) Looking after children (leave them with grandparent or a creche)
3) Helping other groups of people (disabled, elderly, etc.)
4) In the UK, shops selling second hand goods (most are run by charities)
5) Fund-raising for any of the above.
Thinking about it for almost all the above (including other people's answers) I think the more is done by the amateurs the better (e.g. its better to play sports than watch pros).