A good flashlight ought to be mandatory for everybody's keychain. In the past, I used those cheapo mini flashlights that you can get at any toy store for € 2,- but the problem with those is that they fall apart as soon as you look at them, and the batteries are empty by the time you've left the store. It was time to cough up some coin and get a decent one.
After some research I found the Fenix E05 R4, which was € 24,95 and throws a good amount of light with just one AAA battery.
Fenix has a reputation for making excellent flashlights and this one is no exception. The E05 throws a decent 30 lumens of light with a duration of about 2.5 to 3 hours with a normal AAA battery that you can buy pretty much anywhere. I know there are AAA flashlights that are much fancier and throw even more light, but they are at least double the price and don't have the specific feature that this E05 has, and even this 30 lumens is already super bright!
Most flashlights have a real bright center "hotspot" with lower light around it. The E05 has a special diffuser lens in front of the LED bulb that spreads the light out evenly over a large area, which makes this light much more useful than most other flashlights in my opinion.