Since you are doing lots of long training runs I'd just take note of what you fancy when you are really tired and aim to have that available on the day.
On ultra distance efforts I think you just need to eat: it sounds obvious but the thing is it's often not easy to eat so whatever you CAN eat is the ticket - whatever it is!
Drinking High5 is a good way to get extra carbo-calories in easily but eating pork pies, donuts, boiled potatos etc is also fine I reckon.
I remember a cup of tea and a ham butty going down very well before South Barrule in the Manx Mountain Marathon one year