Well, depending on the type of climb and weather it’s harder to eat stuff like trail mix with gloves on. Bars of some sort you can keep in your coat, find them, and eat them easily. Power bars are a no go in the cold, you’d lose teeth trying to eat one. There are other bars that would work though. I tried the MetRx bars and they were OK.
The other thing is it’s just one or maybe two days and it’s not going to add up to a pinch of shit physique wise considering the activity level of climbing. I think the fats in a Snickers will give you some longer lasting energy, the sugar will give you a quick blast, and there is a tiny…make that miniscule…amount of protein too. I don’t have a Snickers for reference but a Baby Ruth has 14 G fat, 38 G Carbs, and 4 G protein.
When I go on long term adventures like my two week archery elk hunt I take trail mix and jerky to carry in my pack. I buy the stuff in the bulk bin that has lots of seeds, nuts, and twigs, and add some dried berries. I’ve noticed that doing that keeps me from losing so much weight. One year before I did that I lost 14 lb. on one hunt. Now I only lose maybe 4 lb. in the same amount of time and doing the same activites.