Theft in order to help others is more likely to be acceptable than if it is for only your own good.
To steal a bus and save others is morally preferable to stealing the bus to save only yourself.

Ultimatly, in an emergency, it comes down to "afterwards would a reasonable person and/or a police officer regard my actions as acceptable under the circumstances ?"

Remember that you may later be called on to justify your actions. In civilised countries, the courts usualy take a lenient view of actions taken in an emergency that would in normal conditions be a serious offence.

In the UK you can expect to be recorded by someone's mobile phone, and posted on Facebook as soon as the power's back up.