Small PV modules can indeed be very useful as disscused in the previous posts.
I would however suggest GREAT CAUTION, and considerable practice and experiment before becoming unduly reliant on such during an actual emergency.
The claimed output of some PV modules is in "chinese watts", and even the reputable ones will only produce the claimed output under ideal conditions.

As an example, consider the charging of 4 high capacity AA cells each of 2.5 amp/hours.
They take more than 2.5 A/H to charge as they are not 100% efficient, 3.0 A/H might be reasonable.
At a charging voltage of 6 volts for 4 cells in series, we need about 18 watt/hours to fully charge the cells.
If the charging circuit is about 80% efficient, then we need about 23 watt/hours of PV input to charge the cells.
That would probably take most of the day from a 7 watt PV module, remembering that the 7 watts is likely a peak at noon, not all day.
In dull weather it might take some days.

I would urge a practical test as follows.
Take 4 high capacity AA cells and fully charge them useing a good line powered charger.
Put the cells in an incandescent flashlight and run them down, notting the run time.
Now charge the cells from the solar charger of your choice, under the conditions in which you expect to use it.
Repeat the run time test.

You may be suprised !

PV can certainly be useful, but beware optimistic claims, hopes and assumptions.