Imagine this, it's two weeks after the SHTF and you running low on AAs and there isn't a D cell around for 200 miles without a paranoid trigger finger between you and it. Your Maglite is dead, your comms radios are about to be done, and smoke signals draw too much attention. If you haven't thought about this before, then how about now?
The following chart shows FRS/GMRS and allowed wattage by channel. The lower frequency ranges from 467.7125 down to 462.5625 are set to lower transmission wattage making them excellent for close range communications. The higher frequency ranges from 462.5500 through 462.6500 and 462.7200 through 462.7250 are open for 50 watt transmission rates allowing for further distance with frequency 462.6750 reserved for emergency transmission. Repeaters triggered by CTCSS tones can be used to greatly increase the range of communication by prefixing the CTCSS tone when transmitting to trigger the repeater to listen and rebroadcast.
Here is a prepper's guide to ammunition calibers and their imperial or metric sizing.