I'm not in the contest but am making a PA story anyways as I'd set out to do so prior to the announcement (that I missed alas).
If it's any help there are some storylines you could explore.
Family trapped in the city, maybe they'd made some preparations but need to venture out into the city?
Well-prepared survivors fend off the raider hordes? Good for combat sequencing and action.
Or maybe write it as the bad guys trying to survive as raiders?