I have a mirror on all of my bikes, find them indispensable. These days LED bike lights are improbably bright and run for weeks. For lighting up the road in front of you, you want something like a good LED torch and mount. For being seen, a little lightweight flashy blinker should do fine at both ends.
This is my favourite mirror: https://www.amazon.co.uk/gp/product/B011DLUBIK
It plugs into a bar end, tightened by an allen key. Should work with flat bars as well as regular road bike bars.
Strong and stable.