Build Your Own Solar Power Generator for under $150. – Solar Burrito
Here is a really good link to a description on how to build a working 12v solar panel charger. This would be very useful during a power outage. It might be a bit heavy to include in a Bug Out Bag. However, it could definitely be included in your vehicle. Speaking of vehicle, it would be good to modify the circuit to allow for you to charge the battery in the case from your vehicle.