high vis jacket when i ride at night. during the day, i wear leathers.
Early morning and at night wearing a reflective vest seems to make a positive difference with drivers, who seem to give me more room. Otherwise, dressing like a construction cone is not any guarantee of being seen. Let's face it, some drivers have broadsided transit buses, large trucks and trains. Inattentive driving will not be fixed by hi-vis. What you wear may make no difference to a driver that will look right at you but simply sees right through you.
Read a bit about inattentive blindness. We often do actions on autopilot, and driving is no different. If the a driver's eyes and therefore brain does not register anything substantially different from past experience, autopilot continues. By being smaller a bike is not a threat to the car driver and therefore does not overcome the attention threshold. The driver's brain filters out the image of a bike, pedestrian, car or other object, even if the bike is right in front of them, and walla, they crash into something they really should see. Maybe they really did not see the object? The foibles of human physiology are complex and deeply ingrained, and will not be completely solved with hi-vis.
Wear something that has crash protection, shields you from the weather and is comfortable. As for colour, wear what you like, which for me is leather or mesh (summer).
If you are riding in a group and end up in a ditch. Somebody will see you, hopefully.
However, if you are on your own(Motorbike, Mtb, hiking, camping, etc) Something similar to a Fox whistle might help you. Goes further than shouting.
3 blast is the International signal for help.
Great in theory but the import cagers don't know that they are supposed to be in the right lane except when passing...
Sorry, but I resent that, I'm what you would call an 'import cager', moved to this beautiful country at the tender age of 28.
Growing up in Belgium and learning to drive there...rest assured I know to stick to the right lane unless I'm passing somebody.