Prepare to get fed up of food very quickly and want a change. On an audax people will eat sweet stuff initially, but quickly tire and move to more savoury, or a mix.
Cereal bars are a good alternative to energy bars, and cheaper - but the companies seem to be under pressure to reduce calories, which is the opposite of what you need. Buy a mix, the same flavour quickly becomes wearisome. I sometimes drink flavoured milk at breaks, I like strawberry, but a lot of people go for chocolate. Also drinkable flavoured yoghurt. Crisps, nuts etc help to replace salt.
A common complaint on long rides is gastric distress. Your body prioritises your muscles for the available blood supply and your digestion rebels. That can present for me as a slightly sick feeling and a feeling I don’t want to eat. One of the few things that always works then is eggs, preferably scrambled on toast. That means finding a cafe prepared to make it for you, but especially in cold weather I find it extremely motivating to get some hot food.
I bought a musette in a yellow hi viz colour for a long ride and it was remarkably handy to carry stuff I needed immediately to hand and to carry food. I used it all the way round, but don’t recollect seeing anyone else with one.