A number of backpacker water purification-filter units are available. They brag that you can turn toxic waste into clean drinking water. The one I own weighs less than a half liter of water and will filter many liters before one needs to change the filter. One could also add water purification tablets to the filtered water.
The scenario involved a "bug-out pack". This implies you are bugging out. If I was to sit on a roof in the middle of a disaster, the cell phone won't work until I got off the roof and moved away from the disaster. If you are walking-driving out of a disaster area, you would eventually get in range of a repeater.
The radio I have uses only 2 AA batteries and they last for many hours. A couple extra batteries don't weigh a lot. I don't typically use a flashlight because they interfere with my night vision. You'd be surprised how well you can move about in the dark once your eyes get adjusted. I also have several tiny LED flashlights, which weigh next to nothing and the battery lasts for dozens of hours, for reading maps, etc. in the dark.
