The Chorus of Pigs can have as many people as you want. There's also the scene in Act III, when the Hero finds the Wizard's magic wand. You can make chicken wings out of yellow construction paper or, if you happen to have a yellow feather boa, drape it along your arms, A chicken beak can be made out of construction paper too. Just tie it on like a mask. A wizard's turban could be a large fancy scarf wrapped around your head or a cone-shaped hat painted with stars and planets on it.
Old bathrobes come in handy for both wizard clothing and royal robes.
THE HERO A hockey or football helmet works well for the Hero's helmet. Add a paper visor if you like. One way to do the Giant is as a very big puppet. His head can be made from a large paper bag stuffed full of newspapers. Put this on a tall stick, add a cross bar for the shoulders and dress him up in an old coat, large enough to conceal the person underneath who holds the stick.