A Steam Community Group Announcement has word on exclusive content for those who buy Galactic Civilizations III through May 17th, offering a few days leeway after the space strategy sequel leaves Early Access on May 14th. Word is this pack of ship parts will never be offered again:

As a bonus to all of our Founders, Early Access players, and early launch weekend adopters, we’re giving away a free pack of unique ship parts to use in customizing your starships.

The Launch Weekend Ship Parts DLC is not and never will be for sale, and will be automatically added to your Steam account when it becomes available on launch day, May 14.

Everyone who has already bought Galactic Civilizations III, or who purchases through May 17, will receive the ship parts as a token of Stardock’s appreciation.