Yes. It goes back to pagan traditions where children would dress up as malicious spirits and characters from folk tales, go round the houses and perform tricks or sing in return for gifts or food. The act of guising (look that word up and you'll find the complete history) as the spirits and characters was intended to blend in with any spirits wandering on Halloween and protect the children from them. The jack o' lantern was originally a hollowed our and carved turnip with a candle inside carried by the children as a lantern. It was common practice Ireland as well I think.
No. In the interests of environmental friendliness, reducing my carbon footprint, and ensuring that waste is kept minimal the treats this year will consist of pumpkin seeds