Bonk-proofing a marathon?

I've always been a little shaky about being able to avoid bonking at
marathons.

When I last raced much I did figure out how to do it right---eat and
drink at every station.

But I had a couple experiences recently on long, hard ski outings that
make me wonder again about this stuff.

I went out for a hard 3.5 hrs a few weeks ago---and I went thru 2 big
bottles of electro-sports-ade plus 2 gels plus a Hot Pocket and a
Clifbar---and I felt VERY wobbly at the end. I felt best for the hour
after the Clifbar and Hot Pocket---eaten at same time. I had about 3
gels, one with caffeine, in the last 1.5 hrs---they seemed to have
very little benefit.

A week later I went out for an even harder 4 hours---2 big electro
bottles and 3 slices of cold pizza (no gels, no bars)---and I felt
fine the whole time.

This makes me wonder if maybe fat/protein is something that I need to
take more of for rock solid long ski outings. But how would this
translate to a marathon race? Neither of my 2 long days were at race
pace. Could one benefit from a slice of cold pizza during a long race?
Would ya just puke it up? Maybe there are gels that have fat/protein
in them? And what part of the pizza was helping me, the fat or the
protein?