Meat pie is just what it sounds like: seasoned beef in a pie crust. Other popular foods in Australia are Vegemite (a yeast-based spread) and Pavlova (a pastry with whipped cream and fruit).
A didgeridoo is made from a medium-sized tree branch that has been hollowed out by termites. People then cut the branch off the tree, and carve one end into a mouthpiece. Blowing into it produces a droning, buzzing sound.
Footy(the common name of Australian Rules Football) was created in the 1850s. It's similar to rugby or American football, but players must bounce the ball, and try to kick it through goalposts at the ends of a field.
The Australian flag is blue. In the top left is the Union Jack, the British flag. On the right is the Southern Cross, a constellation near the center of the sky in the southern hemisphere. On the bottom left is the Commonwealth Star.