Carrying multiple, redundant light sources was a learning process for me.
Back in the mid 1980s (probably 1986 or so), I was in the shower in the locker rooms of my college when the power went out to the whole campus. It was night, but in the fieldhouse it was pitch black inside without lights even in the day time. I had no way to see to navigate back to my locker, get dressed, and get home. It actually happened again a few months later, but that time I had a mini maglight in my locker. All I had to do was find my locker!
Thereafter I carried either a mini maglight or the version that takes AAA batteries in my book bag all the time.
I was fine until a few years later when I was in grad school at UC Berkeley. My office and lab were in the basement of an old building that once again was pitch black without artificial lights. I didn't worry much about it, but I knew I had my little AAA mini maglight just in case. The day the power went out throughout campus and that side of Berkeley, it was DARK down there.
That's when I pulled out my trust flashlight and turned it "on" only to find . . . the batteries were dead.
Since then I've always had multiple sources of light on my person. I started with UK4AA lights from Underwater Kinetics, then went to Streamlight Scorpions, and now I always have the following on me:
Two (2) Surefire G2 Nitrolons on my belt
One (1) UK2L in my pocket a pocket organizer in the cargo pocket of my pants
One (1) Photon LED that wear on the chain around my neck that also has my crucifix and 4-way medal
One (1) disposable lighter, also in my pocket organizer
If I know I'm going out at night or where it might be dark otherwise, I augment the inventory above.