another recommendation for Proviz. I have the coloured jacket now, which is better during grey/cloudy days and still amazingly reflective at night.
For bells, trigger bell is good as it fits under the handlebars and is easy to reach without taking your hands off
triggerbell.com/
there are some really good German brands for baskets and racks and panniers that are interchangeable, depending what you are doing. Look up Racktime racks and all the luggage that goes with them for rear racks especially, and KlickFix mounts for the front. I like that i don't always have to have the baskets/bags/panniers on, so they don't get caught in the racks with other bikes - I can just choose what I need for a particular journey.
you can get lights that are rechargeable by USB, which can be handy as extras. I have dynamo lights, but keep the USB ones just in case.
If you get bike insurance, they might require you to have a silver or gold standard rated lock. Abus locks are good; I have the folding one as I thought it would be easier to get it around objects, though I'm not sure it is. It is handy though. A D lock by them is also gold rated.
Lots of helmets around. Some are folding - Closca - that make it easier to fit into a backpack or bag to carry with you, if you don't want to leave it attached to your bike.
Gloves are really hard to find. I find my hands get a bit sweaty, and then no matter how good the gloves are, thinsulate etc, the lining sticks and I can't get them back on if I take them off. I've tried silk liners etc to help, but no good. I've just ordered some with some sort of Fusion technology that is supposed to help. So I don't recommend any that I've tried
Decathlon is good for cheap silk liners though, and in children's sizes which is good for those of us with small hands! They are generally cheap and good for a lot of basic bike stuff.
A chain cover is good - if you have hub gears, Hebie Chainglider is an aftermarket one that totally covers the chain, so it keeps it clean and with less maintenance, and then you don't get clothes caught in it either. If you have normal gears, there are probably other versions that do the same thing.