what should I do with the multiple domain names we've purchased?

I have a client's site all set up with her good domain name.

Also purchased 4 or 5 other domains, basically her industry name followed by a local city name, ie., promotionalproductsonoma.com, promotionalproductspetaluma.com,
promotionalproductshealdsburg.com etc.

What should I do with these domains? Permanent forward? Build single city landing pages that are part of the main site? Suggestions, please.

And please ignore if this is too off-topic, too non Wordpress.

Thanks!