This year brake problems were common due to the muddy conditions after Rhodes. Organic/Resin brake pads are definitely to be avoided as these will wear out in a couple of hours in muddy conditions. Make sure to use Metal/Sintered pads and be very specific in insisting on this if you rely on your local bike shop to fit new pads. My recommendation is that you buy the correct pads and fit them yourself before the event (YouTube will have instruction videos for your specific brakes). This will make sure that you can change the pads yourself and also that you have the correct pads for your brakes. Carry at least two sets of spare pads with you.
Also quite common were brakes that had not been properly bled. This shows up when the bike is inverted during transport, fixing a puncture, or other trailside maintenance. When the bike is back on its wheels the brake lever goes all the way to the handlebar. This is caused by air in the system which travels up the brake hose and into the caliper when the bike is upside down. If it is the front brake this can usually be resolved by repeatedly pumping the brake lever. The rear can be more difficult but standing the bike on the back wheel while pumping the brake lever will usually work.