I haven't yet done Old La Honda - coming from NYC, those climbing numbers scare me (we don't have any meaningful climbs close to Manhattan). The biggest I've done on the peninsula are Jefferson Ave in Redwood City and Pescadero Creek, in preparation for Coleman Valley Rd in Sonoma (as part of Levi's Gran Fondo). I'll get to Old La Honda eventually.
However, one thing I've learned, beyond the volume and types of food, is also the timing of when you eat. I try to eat something before I'm tired, hungry, and lethargic. For my typical NYC ride, that means 25 miles in at the turnaround point so that by the time I've hit the first return climb, electrolytes and sugar are starting to hit the bloodstream. I've done the ride on just water, but that's left me miserable for the second half of the return trip.