Archetypes are commonly used and easily recognizable characters, motifs, themes, or anything similar. They are not used as much now, or if they are used, it's usually in an ironic way to make fun of them.
They wanted to steal from Polyphemus and retreat quickly because Polyphemus is a cyclops. He showed Odysseus and his men hospitality but soon turned hostile eating two of Odysseus men. Basically they wanted to leave so they would make it out alive.