I've not done the 100k but I have been part of the support crew four times. People walk, people run, people do a combination such as walk uphill and run the rest. The last team I crewed for came third in their category and adopted that strategy.
Support crew is really important too - a few suggestions:
- get some cheap plastic crates, one for each participant. That way it's easier to find people's stuff. It can get hugely mixed up if you just chuck the lot in the back of a car. It also makes it easier to swap gear if you have more than one support team
- have several different phones within the team, that way if one network doesn't have a signal then another one might
- be prepared for all eventualities as best as you can - weather, blisters, etc.
- have a variety of food. Gels and sweet stuff may get really tedious after a while, so have savoury stuff too. Many teams take a camping stove to cook soup and so on, although the gurkhas provide hot water at some of them. Super quick teams don't do this and just hand over a "Grab bag" but unless yo're one of those I think the mood lifting effect of a good hearty meal is well worth it
- scout the checkpoints with your support ahead of race day. They may have changed since I last did it but some of them can be difficult to find, and others (from memory 1, 5 and 7) were tough to access due to sheer volume of traffic. You may decide to skip some of these because of this. 7 had hot food provided so was less of an issue (it was off a single track road so tough with cars going in both directions). 5 was ok to get to on foot but not in a car, so we made sure we knew what the team wanted and carried that to the checkpoint on foot from where we could park. All this may have changed by now as it's a few years since I did it but you'll find out if you scout it. The info booklet isn't always accurate as I recall!