Although it has input from three ultra runners, this list may not be comprehensive and obviously it changes depending on the course (loop, trail etc), distance between aid stations, weather conditions, your own preferences and so on. The main thing is to take a really good crew who will be in charge of:

Anti Chafe equipment eg corn starch, petroleum jelly
Food (medicinal) eg licorice and ginger candy (good for digestion)
Food (nutritional) eg rice pudding, sweet potato, watermelon, baby food, lollies etc
Lime (to squeeze in your water)
Caffeinated drinks
Coconut water/ Maple Water
Ice: for your drinks and hopefully not an injury!
Spare insoles
Gel cushions
Compression socks, shorts, pants etc
Wet weather gear
Heel lifts
Multiple pairs of tried and tested socks and shoes
Cramp stopping pills and potions
Pain killers
Charcoal tablets (for upset stomach)
Mp3 player
Head lamps
Motivational quotes
Salt tabs

Grahak Cunningham is a motivational keynote speaker and four time finisher of the 3100 mile race. He lives in Western Australia.