Establish local museums of ads that once dominated the area. Arrange the rooms by decades. Go down memory lane to see what society was like, where people thought the future was headed, what their hopes and dreams were.
Historic ads are a good representation of what society was like at the time and what people's hopes and dreams were. Ads are representative of the time because:
they promote solutions that people supposedly should want/need at the time
they speak to people in a way that would be effective/acceptable at the time
they promote solutions that are new/modern and represent "the future" at the time
Old ads are also a good way to go down memory lane and remember the "good old times". They were designed to get embedded into your subconsciousness which they probably achieved. If you remember the ads, you will remember the times/circumstances surrounding them.
An actual museum that people can visit. Have separate areas arranged by decades. For each decade show artefacts like shop signs, parts of known billboards, photos, videos of the ads, flyers, etc.
Talk to local people, have them list the most memorable brands and products of their youth. Get in touch with the companies they list and ask for old photos, footage, artefacts, etc. for the museum.
Have the project co-funded by the surviving companies whose ads you were able to collect and intend to put on display. They would have a direct economic benefit and thus interest in seeing this project built.