There's actually a couple of little secrets in the game; if you open up Options in the Main Menu it will show design blueprints for the Maus, a 188-ton tank built near the end of the war. And if you open the Credits in the main menu, it will show a line of Mauses.
How to get 300 Bonus Points Easy: In the shop-screen, click on the "profit meter" (The thing on the top-right that shows how much money you will have left-over if you buy something). and on the gliders page, click below the last item on the catalog, and you'll get The Brick (And more bonus points.)