Participants are not required to carry any specific equipment BUT each racer is expected to have an adequate amount of food, clothing, and outdoor gear for the duration of the race. Racers should also be prepared for unexpected encounters with ankle-deep open water, and should carry appropriate gear to deal with getting wet. A change of clothes and socks may save some of your appendages, perhaps your life. Race officials will do their best keep track of racers as they travel between checkpoints, but this my no means implies that they are prepared to take care of someone that packs recklessly light and is ill-prepared. Such behavior is unfair to other racers.
Strongly Recommended Gear (the necessary stuff):
Tips for Ultra Racers
The Susitna 100 website has a comprehensive list of tips for bikers.
The Susitna 100 website has a good discussion about sleds vs. backpacks, and classic vs. skate skiing, etc.
The Susitna 100 has a bunch of pointers and tips for people traveling by foot.
Shoes - normal trail running shoes are sufficient. Choose a tread pattern with a lot of negative space, which helps with traction in loose snow. Avoid shoes with lots of ventilation near the toe box; they could lead to numb toes in extreme cold. If you're worried about cold feet, maybe get a 1/2-size larger and wear thick or two sets of socks. Gore-tex shoes are not necessary and can lead to sweaty; and therefore wet, feet. Interior snow conditions are usually fairly dry. In cases of fresh snow, very lightweight gaiters like Dirtygirl (made for summer sand and gravel conditions) can keep snow from getting under the tongue, melting, and leading to wet socks. www.dirtygirlgaiters.com
Socks - bring several extra pairs they are light. Fresh, dry socks can be very invigorating.
Cleats - Cleated shoes are unnecessary. Areas of ice are usually short and walking carefully over that section is often sufficient. However, overflow areas are sometimes uneven, and in those cases rubber slip-ons with cleats like Gripons and Stabilicers are light and quick to put on and take off. Yak Tracks can be a little too much and uncomfortable to use with running shoes.
Clothing - Layers with zippers or buttons for quick ventilation are nice to prevent sweating as your body cycles through warm/cool spells in cold conditions. Eating tends to first cause cool extremities as blood flow goes to the stomach, quickly followed by a resurgence of blood flow to fingers and toes and quick warming. Wool gloves and hat work better if they will get wet, but synthetic layers are lighter and easier to layer.
Light - the smallest LED headlight gives sufficient light for running. Snow is very reflective and you will not be traveling so fast that you need to see very far in front of you. On the other hand, many newer headlights have multiple settings, and a strong spotlight is convenient when you think something unexpected and unlit, like a moose, is ahead of you.
Sled or pack - sleds let you carry more gear with less weight on your back, but can be annoying if not well designed and tested for your running style and cadence. If you sled, practice with it on a variety of surfaces: hard pack and fresh snow, and terrain: flat, hills, and bumps. The bumpy surfaces snow machines often create can be particularly trying with a sled as it is constantly pushing and pulling on your waist over each bump. When designing your sled, remember that different materials shrink different amounts in the cold, and some become fairly brittle in extreme cold. Bring tools and quick-fix materials like duct tape, wire, and cord. If you pack, practice with it properly weighted and distributed. 10-15 lbs of gear on your back will probably chance your running form.
Overflow - the state of overflow can be deceptive; sometime solid and hard, and other times wet and slushy. The current temperature has no obvious bearing on its state and wet overflow is as common in -40F as +30F. Plastic bags over your feet are an option when in doubt or just to be safe. If you're wrong, this is a prime opportunity for using a pair of those extra dry socks you brought along.