I've always done some form of voluntary "work", but very different types at different points in my life.
In my 20's I was a special police constable for several years. Obviously, very strict adherence to rules/laws, attending obligatory training courses, but very flexible as to what work you actually did. I could (and did once) literally turn up unannounced and unplanned in the parade room at 10pm on New Year's Eve to do a night shift - the sergeants were always fine with an extra pair of hands! But, if you'd put your name down for a specific duty, then you'd be expected to be there (barring sickness of course).
I've also been a long term "observer" for our local group of advanced motorists (now in my fourth decade doing it), where you go out with a "normal" driver to help them learn advanced driving techniques and help them prepare themselves for the advanced driving test. At different times, I've been treasurer or secretary of the local group.
Currently, my main focus has been on our village library. I started a group about 20 years ago when it was first closed, initially to get the council to re-open it, which we achieved, but then it was closed again a couple of years later, so we took it over and now operate it ourselves, no paid staff at all, just a group of volunteers from the village. In particular, it's been very useful for our village teenagers to get work experience to count towards their cv, uni application, DofE award scheme, etc. All our volunteers do the "proper" job, i.e. they're trained to learn and understand the computer systems, and other procedures/rules, work on the desk, supervise/train people using the computers, etc, certainly not just to brew up or tidy up etc.