Extending the frequency range of CB radios might be a good thing for a SHTF situation, but I would strongly suggest not transmitting on those extra channels. Boosting power a bit in the radio might be all right depending on the model. The problem with CB amps is the lack of filtering. You can spatter the whole spectrum with harmonics with a CB amp, and create damaging disturbances. That would be a great way to draw attention to yourself, and the fees are in the ten-thousands of dollars...
If you want more bandwidth and power, look to amateur radio. Anyone with $15 in their pocket can study a bit and pass the exam, at least Technician and General classes. Kids in primary school do it... It's super-cheap, very easy, no excuses. Ebay is littered with cheap amateur gear, often costing no more than a new CB radio.
Gil.