Please take the following into consideration, especially if your cat / kitten is new to your home…
Even the most social cats should be kept in a separate room during trick-or-treat visiting hours. Confine your cat to an inner part of the house or set up a barrier to the entry-way to avoid an unintentional escape. Constantly ringing doorbells and shouting trick-or-treaters are frightening for many cats, and once out the door, your cat may be difficult to find and retrieve.
Do not force your cat to wear a costume. Most cats find wearing strange clothing stressful and upsetting. Stress and cats simply do not go well together. And Halloween is already stressful enough for most cats without adding insult to injury.