We got some options. Let's start with low-tech and work our way up. Also, as a baseline, we're taking Usain Bolt's records, who did the 100 m dash in 9.58s, which is about 23 mph. Obviously, most people do not come even close to this speed. Marathon runners have covered 1 marathon (26 mi and 385 yards) in 2 hours, 45 minutes, and 46-ish seconds. That's 9-ish miles per hour.
Your boots/exoskeleton of speed can be made of a some springy material which allows them to hop like a kangaroo. The nice thing about hopping is that your previous hop can contribute to the energy needed for the next hop. This makes it potentially more energy efficient compared to other forms of locomotion. A "comfortable" speed for a red kangaroo appears to be around 15 mph, with a maximum of 44 mph.
Cleats or Snowshoes
Your boots of speed could just provide better traction over rough terrain. As Lindybiege hilariously relates here, hobnails and cleats improve your grip, which in turn can improve your speed. Not exactly an exoskeleton, but you can take more direct routes and therefore move more quickly than normal.
What About Stilts?
As seen on the records, stilts do not actually help people move faster, despite the increase in stride length you can get from them. Worse still, stilts are powered by the people using them. (For instance, the 7'13" world record for running a mile? Not impressive.) No, stilts will not help you move faster unless they're powered by something.
There are some design issues with powered exoskeletons. It seems most of them are designed for either heavy lifting, or to help the disabled. Most products out there are not designed for speed. If you would, you would find they are:
- Very Energy Efficient
I would go with a solid state battery, which stores electrical energy really well compared to many other batteries, and could be potentially recharged by solar arrays. Some simple linear actuators or hydraulics could help get some speed in those legs, but both of those are relatively slow.