My daughter and I walk to and from school daily and we always wear Hi-visibility vest during summer and Hi-visibility jacket during wintertime. Safety is the main reason for this, as wearing such clothing could add high visibility for motorist especially on dull days.
The good thing about hi-visibility vest is that aside from being a florescent color, this has reflective stripes that would reflect lights from vehicles and bike head lamps. This vest can be worn on over a shirt on warm days or coat on cooler days.
A high visibility jacket or hi-vis parka ideal for autumn and winter, as it is really warm inside and has a waterproof outer shell. I have one of this Hi-vis padded parka and I can tell you that it is really warm!
Pictures of hi-visibility (reflective) vest and jacket are shown below. My daughter and I have these type of Hi-visibility clothing, but these can also be bought of different styles and colors.
Here are some other reflective things you can get:
Hi-vis arm bands, ankle straps, reflective body belts, and Hi-Vis backpack cover.