You can take a look to that page; to my great surprise this fitness program is available online.
I am far from having done any special forces test, but here is how I see it.
1. The more you are in shape the more you increase your chance of success.
2. If you are like me and you are not quite impressed by those 13k rucksac walk, then do more. Both american special forces and SAS are doing much longer walk...
2a. As you can see from yourself, while the performance required is quite impressive, it's high but not olympic; and so is the training program.
2b. Don't be shy to as your PSP for customized program after a point, or reinforcing key weak muscles (i.e. forearm)
2c. At some point you will need a training program that is more intense, and there is a LOT of training techniques that have not been touched.
3. Avoid at all cost injuries. Make the difference between a lactic burn from a real injury
3a. While it's true that most of our limits are mental, you need to have your muscles well developed before going to far (My personal experience)
3b. Go progressively; look for fitness not for lesion.