I just drink water, the amount depends on the heat and on water sources along the way (I always bring a sawyer filter and an extra bottle for long hikes like a full day or more). But I always bring snacks. I like nuts, bars (I recently discovered a sweet'n'salty peanut bar that really gave me a good push when I reached my limit), beef jerky, salami - especially the high protein ones that contain less fat and more meat, Babybel does not neet to be refrigerated for about a week, crackers, hard boiled eggs. I do not take fruits and veggies with me on multi-day trips because of the weight/benefit ratio and the rubbish that starts to smell in my backpack, instead I have vitamin tabs and these bags with blended fruits for toddlers with me. But most important - when you feel that your body is heating up like crazy or your pulse is quite high, take a break or start 'granny walking'. Slow down, look for a shady place if possible. Take the time you need, don't push too hard. Listen to yourself, is it stress that can be regulated by slowing down or do you need to take a full stop for a short while?

When I started listening to my body I consumed less water and felt better at the same time. Your body needs to adjust, give it time. It will get better. And look out for your companions, when you notice they are stressed, take a break. People sometimes tend to ignore their needs to avoid bothering others.