The best type of maid of honor is like a boyscout always prepared and always helpful. To earn your merit badge, put together a bridal emergency kit, full of those oh-so-useful things everyone seems to want on the day of a big event. but no one has except you! Brides, in case your maid-of-honor prefers boy watching to boy scouting, you could either ask someone to help you put this bridal emergency kit together, or pull it together yourself.
Sewing Kit, including safety pins and small scissors
Clear nail polish (helpful for stocking runs)
Nail polish in the bride's shade
Makeup (you'll probably have this there anyway!)
Straws (for drinking without messing up lipstick
Brush and comb
Bobbypins and hair elastics
Baby powder (also useful for getting out last-minute spills on a white dress)
Eye-drops (look for redness reducing)
Contact lens solution
Tampons and pads
Headache medicine (bring two different kinds in case one of the bridal party is allergic)
If you're getting dressed in a place that won't have a bathroom near, you'll also want to bring a mirror, bottle of water, and moist towelettes.
Good extras: charged cell phone, camera for taking getting dressed candids, list of vendors phone numbers, wristwatch.