Lael Wilcox used to drink half and half (easily found at convenience stores, high calorie, high palatability, fast). I tried this trick and found that it made me fart more than I found acceptable.

Lael has since stopped doing the milk thing since apparently it aggravates her asthma.

I like food that softens quickly in the mouth. Lil debbie oatmeal cream pies, brownie bites. Absolutely no sour candy or spiced nuts ever. Real Food(TM) is nice but I save it for when I'm at a resupply. Other athletes vary.

One thing I love about the ultra bike world specifically is how unique everyone's systems are. In other cycle disciplines the gear and methods converge tightly, but in umtb it's all over the place.