I've done some ultras and a few marathons, eating stuff varying from hot dogs to peanut butter and jelly covered in gel. It's going to really be up to what he responds well to, so a lot of experimentation is in order. I love Hammer products, as they're sugar free but still very high carb and in my experience, easy to digest. Their Endurolytes seem to work well as an electrolyte supplement. Maybe before the race, try to find out what will be offered and at what miles, so he can test the available supplements.
This may sound a little weird, but to train for ultras I used to run for 3-5 hours totally fasted, I heard from other ultra runners that this helps your body get more used to using fat as fuel. It seemed to help keep the bonk away. Also, caffeine is supposed to get you burning your own fat quicker and seemed to work for me.
^For the above, I can't and won't try to quote any scientific study or whatever to validate it. Worked for me, may or may not work for others.
I wish him the best of luck. Here are a couple of links.