Ask HN: Amazon HQ2 inbound – potential secondary business opportunities?

Looking for advice/experiences from folks who live and work around major tech HQs. Especially interested if you witnessed the transition pre/post HQ. Amazon HQ2 is coming to northern Virginia. They've already started hiring, first 400 employees are expected this year, with 25,000 expected over the next ten years. Other than commercial and residential real estate, what are the potential business opportunities that arise from having one of the big tech firms suddenly in your backyard? I'm curious what people's thoughts are on both the direct opportunities related to marketing/selling services to Amazon, and on secondary markets that arise from additional tech workers. What do you wish you would have known/done before X company came to town?