Keep an eye on the ultracapacitors used for automobile start-stop applications
In every application I've seen, ultra/super caps are used for a quick burst of power, most often for load smoothing, which includes start/stop vehicle starting and , yes, supersound systems. Seconds, Not minutes or hours. So not very useful for emmcomm.
But when I was looking at short-term accumulators for the solar plant that runs my CA station (when I'm having fun and only when the sun shines, which is a lot, over here), the most practical device to smooth out the power flow over 5-15 minutes was a simple 100 A/Hr SLA battery. Not a capacitor bank, or a LiFePo battery (wrong charging curve, high cost), but one of the oldest and least expensive techs around.
But for EmmComm... generators are always in demand by the professionals. And they last long time.
A good choice would be the Honda EU2200is "suitcase generator". It can run an HF station with a 600W amp, or lights and a refrigerator or A/C or an electric heater. The rolling oil fields we are surrounded with provide a ready source of fuel, even in an emergency - and it is very efficient. It is a little pricey. But if you also have occasional blackouts, it can do double duty and is way easier to justify. Just ask anyone from Florida or the East Coast who need power after a hurricane or nor'easter.