You sound like the perfect person to be on or chair a committee! Lots of people go to different societies. They sit and listen to the speaker, enjoy coffee, a biscuit and a chat - and then vanish into the night. Finding people to actually contribute is difficult, but it can be rewarding - especially since you can get to find the speakers you want!
The National Trust has also been suggested and there are so many opportunities there you wouldn't believe! It'd collapse if not for the volunteers. (You get travel expenses and a discount!)
Local councillor? You don't actually need to be party affiliated at parish level in many cases as again no one wants to actually get their hands dirty and do the job, so you may find that in your parish, you'll be grabbed with open arms and co-opted.
A lot depends on your interests. I would suggest joining a few local groups (history society, WEA, gardening, etc), seeing how you get on with the people there and just let yourself become more involved.