I just got my first cargo trailer! Crazy fun.

Before I start hauling anything I really care about (like my pets) or doing trips after dark, I want to make sure that I'm super visible to traffic. I'm thinking maybe an LED/reflective slow vehicle triangle and a flag might be a good place to start (though I haven't been able to find any flags locally, and I have no idea how they attach.)

Anyway. How do you light up your trailer and/or make it more visible during the day?