Here is a Basic Packing and Checklist:
• Pillows
• Sleeping bag/blankets
• Light source
• Toiletries
• Separation of dirty/wet/clean clothes (i.e., garbage bag).
• Emergency costuming: Duct tape, safety pins, spare lacing (especially if your costume is lacing dependent), needle and thread.
• Basic first aid kit
• For PC's all elements of your costume: Shirt, pants, makeup, white headband, armor, weapons, shield, spell packets, jewelry, magic items, treasure, spell book, item tags, pouches, real money to pay for the event.
• For NPC's: black pants/shirt, a good pair of shoes, white headband, or any personal weapons you want to use for the weekend. You may not get to use them all the time (not everything you will play will be carrying a long sword), but if you feel that strongly about using your own weapons, be sure to bring them for when you can use them.
• For BOTH: spare clothing (especially socks), warm clothing in case the weather turns out differently than expected.
• Weapons
• Mirror
• Cabin decorations
• Entertainment, i.e. a deck of cards
• Food
You don't necessarily need all the items on this list, but it is a great place to start from.