One thing to bear in mind with adding our backup knives, locking biners, pulleys, etc. on our PFDs is the additional weight, thus decreased floatation, that we incur when we start carrying the kitchen sink on our PFDs.
Also, there was a recent rescue knife discusson on the GCPBA list a week ago with about 50 posts from riverrunning veterans and newbies alike on how to attach knives, pros and cons of different brands, metal composition and ability to hold an edge, using rescue knives for lunch, an on-the-scene account of an entanglement drowning on Westwater a couple of years ago (stating a knife wouldn't have helped), and just about anything else under the sun. Its in the GCPBA archives if MB's library on the topic isn't enough for you.
An aside, the Wenoka dive knife was mentioned (unfavorably).
Be safe (and don't use your rescue knife for cutting up lunch),
Nothing in the world is more yielding and gentle than water. Yet it has no equal for conquering the resistant and tough. The flexible can overcome the unbending; the soft can overcome the hard. - Lao Tse