Some of the characteristics that makes Fell running very different from Marathons includes the fact that Marathons are run on the road while Fell is run off road. With Marathon, endurance is the main objective of the race whilst Trail running includes endurance and elements of navigation skills. Fell runners usually carry survival equipment  prescribed by the race organiser.

Equipment
Race organisers tends to suggest the best equipment to carry, this usually depends on the toughness and distance of the race, some Fell runners have to carry camping equipment if the even  spreads over days.
For shorter races basic equipment such as a bum-bag to carry you compass and other smaller stuff and a Goretex or any other water proof tops is advisable.

Shoes
Fell running shoes and Trail shoes are quite similar, one of the most important features of the shoes is that it grips well. Shoes with  low midsole and heel are one of the best. Sometimes you need to know the course of the race to choose the best shoes, if there are lot of mud for example you want a shoe with pronounced studs to stop you sliding and falling.

You can find more information about Fell running at British Open Fell Runners Association