During our 2006 Perth to Fort William hike, jarring a knee on Rannock Moor resulted in a slow and painful downhill hobble the next day.
Thankfully, our destination had a pharmacy where we were able to purchase a knee brace to resolve the problem.
However, it occurred to us that if we'd carried a knee brace in the first place we could have protected the injury much earlier and proceeded less painfully.
Consequently, we both carry a breathable knee brace of the type shown. This one was purchased in a local department store and cost under £10.