In the past I've been a Special Constable and have been secretary and treasurer (at different times) of the local group of the Institute of Advanced Motorists.
I've also helped in the local RNLI shop in the past, and helped organise model railway exhibitions, hobby and craft fairs, and done electrical sound/lighting work for amateur dramatics in a local theatre.
Currently, I'm on village groups/committees for running the local library which we took over when the council closed it, the local community centre, and part of a preservation group restoring a closed down theatre.
I also go out group litter picking around our village and surrounding villages and help maintain a local railway station (cleaning, tidying, planting flower containers etc).
Sounds a lot, but most of it is pretty irregular so easily doable around work. Rarely have more than one thing to do in any week, so it's typically one evening and one half day at a weekend.
All very rewarding to be doing something useful and giving the opportunity to meet new people etc.
The only "voluntary" activity that I hated and didn't last long was being a school governor at our local primary school. It was all smoke and mirrors - the head and the local authority representatives ran it as their personal pfieffdom and had no interest in "outsiders" being involved so they constantly manipulated the proceedings at governor's meetings to get their own way, ran roughshod over perfectly legitimate idea/concerns etc from the other governors. Worst was one evening they had a "sham" consultation about "options" for a particular area of the school operation - we spent two hours discussing the relative merits, pros and cons of the two options they had put forward. At the end of the evening, we had a vote, and there was a majority in favour of, say, Option B - only for the Head and LA rep to then say that Option B wasn't actually allowable and the only option was A so "instructed" us to vote A instead. That was a complete fiasco and waste of an evening. I resigned that night, as did 2 other governors. Looking at the school website ever since, it's a revolving door of new governors, none who seem to last longer than 2 or 3 meetings. So much for democracy and openness! Like I say, all smoke and mirrors!