I retired last Sept at 66. I'll tell you what I did and how things have been working out for me
First though apply for your bus pass as soon as you can do, so you have it for when you retire, even if locally there are not many buses, in other places there are and it makes a world of difference.
I discovered that there was an event happening the weekend after I retired so I booked that and hotels for that and some air bnbs for the following week. That sort of took my mind off thinking about it too much. I used my bus pass so much that week. When I got back how wonderful, I could unpack and do my washing and shopping etc and not have to worry about work. Unlike the break I had a month earlier, that was a wonderful feeling.
I jotted down a list of places I thought I'd like to go and exhibitions I'd like to go to and decided that with time limited things I would make an effort to go as soon as I could, even in retirement things come up, so I could manage to get to see them and not having to do it in the last couple of weeks which I'd found myself doing. I signed up for bus trips to places I'd like to go to with the local community bus, I'd already started going on some but couldn't do all the ones I wNted to because of being busy, even though I wasn't working full time. When it started getting cold I spent time doing some reorganization of the house, had it been warm I'd have started on getting the garden into shape. Little by little. Sorting out kitchen cupboards, sorting out clothes, sorting out books and paperwork, and some loft stuff, I got rid of an old Christmas tree and various Christmas stuff so that is slimmed down to what I really like. Not all day, every day, but when I had not much else on. I went to places locally I'd always meant to go to, and enjoyed looking after my dd's dogs without needing to worry about my laptop, so caught up on some reading and a but of knitting. This spring I started getting on top of the garden. At first I often did have lie ins just because I could, I don't any more unless I'm worn myself out doing something strenuous. There is such a lot I want to do! I pace myself. I have gone through all the craft stuff I'd put aside for when I had more time, and made decisions did I want to spend time doing that tapestry kit, as my eyesight isn't as good as it was do I want to spend my time doing that, will I ever use that material, that sort of thing. If in doubt leave it and decide later.
Ive not gone away as I'd planned as have had a bit of a health scare and have wanted to be around to open letters and be able to go for appointments at short notice. I will need an op but it's not as serious as they thought originally.
I'd actually started cutting back on some voluntary stuff that I'd been doing for a long time, and I've not taken up anything new, but like some others I've said OK to some one off things. I might change my mind, but I don't want to replace work with unpaid work. I still do the voluntary stuff I could cope with.
I've not yet joined u3a, local branch doesn't seem as vibrant as a friend's a couple of counties away, but I've not ruled it out. I've done some free future learn courses, and worked on my family tree. I may do some courses in the nearby town, they will be there next year or the year after. Some trips away will need to be put on the back burner while I recover from surgery but once I have I will catch up with exhibitions etc, and then trips away
Its working well so far, haven't been bored or lonely or anything else, like that which people fear. Eventually I'll be on top of long outstanding things to do around the house and garden, maybe. I had a lot of work done on the house so lots I won't need to do, still some outside stuff but it will get done.
Your situation might be very different to mine, if course. Everyone's financial circumstances differ but I have fewer day to day expenses, as have more time. OK I bought a heated blanket and got an oodie but I can use both next year!
I thought I'd miss work but I don't
Whatever you do, enjoy and do apply for your bus pass as soon as you can (and consider going away for a few days after you retire, September weather is often glorious