We have two documents at every gate - a project file audit and a gate approval form. The first is a checklist that shows if the required docs to pass that gate (e.g. previous gate approval, signed-off design requirements, patent review form, etc...) are present, not present, or not applicable. The project manager initials these.
The second lists the requirements (e.g. concept agreed, patent review complete, mfr site decided, etc...) for advancing the project to the next phase with spaces for the decision makers (business unit, engineering, maybe operations) to sign.
These are standard lists depending on project level and gate number. We also have standard presentation formats for each gate that allows the project manager to present the required info to the team/ stakeholders.