The first time I tried a packet (GU gel) in a practice run, I nearly puked. It tastes like liquefied bubble gum and the taste stuck with me for the next 30 minutes. Which ones work well for you?
I used to puke anything I had when I ran.
My digestion couldn't handle food when I was running. It was a mix of slight heartburns (& coffee) causing a sensitive stomach which didn't like food moving around when I ran and partly because I was running so hard my stomach didn't have enough blood to process the food.
Several weeks of eating peanut butter mini sandwiches with their crusts cut off, banana slices and oranges dipped in salt, while running at a moderate pace, I managed to tame the tummy.
That said - I don't think I like the taste of GU gels, but like coffee or beer, you get used to it (& the extra 100Kcal feels like it goes directly to your legs).
Try something like flapjacks or even rice cake [1]. It's more suitable as bike nutrition because of the ergonomics but at the end of the day it's all just carbs.
If you don't like any of that or the solid food is difficult to swallow in a race, you can try just water mixed with maltodextrin. It's a very slight sweet taste.
1: https://www.britishcycling.org.uk/zuvvi/media/bc_files/izone...
Personally, I've switched to mostly liquid nutrition, currently using a custom blend from Infinit. For 6+ hour races, I'll supplment with a PBJ sandwich or a bar of some sort.
And like another person mentioned, it takes some practice to get used to it. A lot of people have trouble digesting anything while running.
I found that just like my legs needed training to withstand a marathon, so did my digestive system need practice to process and retain enough calories. Eating 4000+ calories on a long run day used to be pure torture. But you get used to it.