Incorporation documents and the share register, the shareholders' agreement, yard or premises documents, equipment and material invoices, licences, bonding and insurance certificates, employment records and every contract or bid.
The establishment file is the application file
Hypothetical example: the contractors spend four months setting up and then try to reconstruct what they did. Keep the record as it is created instead, because these documents serve three purposes at once: they show the enterprise is real and operating, they show funds committed and at risk, and they show who controls it. File them chronologically with the amounts and dates visible.
Include the yard lease or purchase, invoices for the trailers, augers, welders and materials, the state and municipal registrations, contractor licensing and bonding, insurance certificates, the first payroll registers, and the signed contracts or accepted bids. Add the corporate documents and the funding trail from the investors' accounts. A file assembled this way needs organising rather than reconstructing.