In a survival situation in the UK (None medical) you would expect to face mainly cold and wet weather.
I carry a fire steel and a woodlore knife (Handmade British blades) Steel in my pocket attached to my belt and knife on the hip.
I also carry a small Katadyn water purifier and a medicare survival sleeping bag. Both are kept in a very small hip bag.
But the steel and knife I would choose if I hand too make the choice. If I had to choose just one I would go for the knife everytime.
I also think it is very important that you are in peak fitness when going out on a trip. It could mean the difference between life or death in say cold wet conditions. Speed is important but fitness can give you valuble extra time in extreme conditions. Frame of mind is also important even on the regular trips.