Dan has already replied, I have some variations and comments.
1. A yellow hiviz jacket for daytime which is reversible and turns into a silver reflective jacket for night time. Looks very effective in the YouTube videos I’ve watched
For both night and day when it rains, I use either a non-reversible hiviz rain jacket with reflective patches, or a bright red cycling cape with reflective patches.
When I don't need a rain jacket, I wear a "Sam Browne Belt", which has a wide horizontal waist belt and a diagonal sash over one shoulder. I started using this in about 1977. My current Sam Browne belt is made of woven fluorescent tissue with strands of silver reflective material so suitable for both day and night. I wear it most of the time when cycling, but generally not in hot sunny weather when I consider that a bright red T-shirt is sufficiently visible. This woven tissue Sam Browne belt is slightly less visible than my previous waterproof plastic ones, but has the advantage of being more permeable so doesn't get so damp underneath with sweat. In France this has the added benefit of ressembling the reflective gear used by French motor cycle police, but I have noticed a lessened effect in the past few years as yellow fluorescent/reflective jackets have become more generalised here.
2. An always on front white and back red light that’s bright enough to keep me seen and not annoy or blind drivers too much. Preferably Dynamo so I always have light and don’t have to worry about batteries (possible problem there would be that they are only on when cycling at a certain speed ? So for example if I’m out in the country and stop at a junction to wait for traffic before I pull out , I have no lights on )
Another vote for hub dynamo, high output front lamp (for example B&M Cyo, Schmidt Edelux) and at least one rear lamp run from the hub dynamo. I have two hub driven rear lamps on my touring and utility bikes, one on the mudguard and one rack mounted. B&M "Line" rear lamp is supposed to make it easier for following drivers to judge the distance from the bike. All these lamps have the Standlight function, so keep shining for a few minutes if you are stopped at traffic lights or elsewhere.
Copying motorcycle practice, I leave the lamps on most of the time, including in daytime, except sometimes in full sunshine on routes with little motor traffic. Until recently, oncoming cars or cars waiting at side junctions generally tended to treat me as a motorcycle/moped and not pull out in front of me, but again this effect has worn off with the generalisation of bright bicycle lamps.
3. A set of front and rear lights that blink on and off , have fantastic battery life for less fuss. I like the look of the little square bontager? I think the brand was , something like that.
I don't personally like flashing lights as I consider they can be mistaken for turn indicators, but I have a relatively big Cateye LD1100 battery lamp that I use as 2nd or 3rd rear lamp. This has an array of bright LEDs, six facing straight back, plus two on each side facing sideways at 90°. The side LEDs significantly improve lateral visibility, which I believe is particularly important on roundabouts. I generally leave it on fixed mode, but very occasionally use the half-flashing mode (5 fixed LEDs and 5 flashing) in very bad visibility conditions (heavy rain). If at all possible, I avoid riding in thick fog.
Anyway , I have also been also thinking about the use of flags , which I had never even heard of until a read a comment online of a guy recommending using a 7 foot flag with different patters. I kind of dismissed the idea as not for me or a bit unnecessary as well as the fact that’s it’s not common or popular over here and don’t know how it would be perceived or accepted by other road users etc. Sometimes drawing attention doesn’t always work out in your favour as road use and attitudes are quite varied and sometimes hostile
Except on a recumbent or a low trailer where a vertical pole flag is a good idea, I don't like the use of flags. I believe the sort that stick out sideways encourages the very small minority of idiot drivers to see if they can pass close enough to touch the flag.
Old-fashioned tent poles mounted sideways across the rear rack worked quite well for me when cycling in England, where cars tend to pass much closer than they do here in France, probably because that kind of tent poles can scratch paint on a car. A foam camping mat carried in the same way is also reasonably effective, as it increases the perceived width of the bicycle without provoking an agressive reaction from the idiots.
Wheel reflectors are now compulsory here in France, and probably in many other countries as well. I consider the flat ones to be nearly useless, as they are only visible through a small angle either side of 90° and I very rarely stay stationary at a road junction at night. If moving, that kind of reflector is generally visible too late to avoid a road junction collision, if a car driver can see the reflectors I am out of his way before the car hits me, if on a collision course the driver can't yet see them.
So to comply with the rules I fit the round SekuClip spoke reflectors. While not really visible from straight ahead or straight behind these are visible at wide angles from side on, so give a bit of useful extra night time visibility in some circumstances, again especially on roundabouts. In the photo, the blue bike to the left has Sekuclips, the Brompton folding bike in the middle has a slightly less effective and older version of the Sekuclip concept (Moonline) and the red bike has the standard flat wheel reflectors, plus a tyre with reflective band.
Apart from the Sekuclips, the other reflectors that show up quite well on the photo are:
- the red rear reflector on the blue bike and the two red/orange reflective strips on the white mudflap of the same bike. I consider these reflectors to be a useful safety aid aimed at following vehicles.
- the white front reflector on the Brompton. IMO this is useless on a bike with a decent front lamp and I only fit front reflectors on bikes because it is mandatory here. They do perhaps have limited use on my (rather wide) trailer, as they could dissuade an oncoming vehicle from overtaking when room is limited. I don't have any forward facing lamps on my trailer.
- one of the pedal reflectors on the red bike. IMO, again pretty useless and only fitted because mandatory here. Pedal reflectors are only really visible from straight behind or straight in front, but in my case often obscured from a following driver by my pannier bags. And I consider that my rear lamps and rear reflectors are sufficient for following drivers, and the best solution for oncoming divers is a decent front lamp with a wide beam.
The most important thing is to remember to take account of the fact that despite having all these lights and reflective devices,
sometimes a driver won't see you simply because they haven't looked properly. This is a particular problem with large roundabouts. Rain and darkness exacerbates the problem, when visibility from a motor vehicle is drastically reduced.