Flares are important. We also have the reflective triangles.
The flares can be seen for a long distance and don't require headlights to be seen, they aren't put out by a little rain and I have used them several times to good effect.
Be aware that they are really HOT and will burn you, clothing, etc. Keep them away from flammable stuff.
After you have moved your vehicle safely to the side of the road: Use a minimum of three. Place one a hundred or so feet behind you down the road, another near your vehicle at the edge of the road and finally another several feet in front of your vehicle so you have all directions alerted.
We carry six.