From the main menu, go to the "Extra Features" menu, highlight "Movie Stills", and then press your Up button; this will bring up a knife and fork. Press your Enter button and you'll be taken to a map called "Trail of the Donner Party, 1846". On the map, repeatedly press your Left button to highlight a trail with dates. Go past Fort Bridger until you reach "Truckee Lake October 30: Donner Camp"; press your Up button there, and another knife and fork will be highlighted. Press your Enter button to see an advertisement for Ravenous Beef Jerky, a bona fide promotional item.
All easter eggs were generously submitted by SirDonk