You don't need to sleep. Focus. If that doesn't work... caffeine.
Cafe feeds? umadbro? You'll lose way too much time stopping for food that's too fatty to be digested properly anyway. I don't know what gels you use but train on them whatever you choose. I prefer Torq and use their bars and gels and drink, for that matter, during 24s.
You'll probably stop less if you're unsupported because there's no one there to listen to you whinge.
Why fixed? Don't you have a proper bike (ooh sickburn fixie skidders!) for triathlon? Whatever you choose, it might be worth having some spares - be a shame to lose a good result because of a mechanical you can't fix.