Belt Life Preserver, Armed Forces History, Division of History of Technology, National Museum of American History, Master Tire and Rubber Company (Manufacturer)
50 Mission Crush Hat, Armed Forces History, Division of Technology, National Museum of American History
The Libraries has many items in its collections and catalog relating to D-Day.
The National Museum of American History also features WW2 objects in its exhibition The Price of Freedom: Americans at War.
Here are some additional resources:
"First Wave at Omaha Beach," Atlantic Magazine, by S. L. A. Marshall
Library of Congress—Veterans History Project
—Elizabeth Periale, with the help of Chris Cottrill