One of my worst backcountry experiences (and the reason I don't go anywhere in the backcountry without my Garmin In-Reach Mini or a hiking parner, or both) was because I went on a solo trip in the middle of July and didn't plan property. I didn't carry enough water, didn't stop tontake breaks often enough and didn't listen to my body telling (screaming at) me that something was wrong. I assumed that I knew what I was doing, could handle it, didn't want that extra water weight, didn't want to stop and add unnecessary time to the clock, etc The net result was heat exhaustion, hallucinations (honestly thought there was a chupacabra outside my tent) and cutting the trip short. Longer term results were a few lessons.

- Drink before I'm thirsty. Eat before I'm hungry. Stop before I'm tired.
- Hydrate. I carry 2L of water all the time and I don't pass water sources without "cameling up" and topping off.
- Electrolytes. I carry Nuun tablets with me and will usually have one or two liters of water with electrolytes added. Worth noting, I only put them in one of my bottles and i stick that bottle in my bear bag at night now. I believe I read that here.
- Food. I tend to *hate* to stop once I get going until I get to camp. I keep a few snacks in my hip belt pockets so that I can eat without stopping.
- Clothes. I carry three pair of hiking socks and change them out regularly. In the summer, I wear very thin clothes that breathe well and have become a Merino Wool snob, especially in the undergarment area. I also try to wear a wide brim hat thats well ventilated. I'll also sometimes drench my buff in a creek and wear it around my neck.
- Pay attention to your body and heed its warmings. You know if you need fuel (food), eat You know if you're dehydrated (no / dwindling sweat, dark urine, faint or dizzy, you think there is a chupacabra outside your tent), drink.

What are some summer backpacking trips you've learned that make the hot weather more pleasant?

Superusers do not speak on behalf of REI and may have received
one or more gifts or other benefits from the co-op.

I tend to hike at a fast pace. Was never an intentional thing, just kinda did it. I think it goes back to when I first started seriously day hiking a few years ago and needed to take a "keep your head down and carry on" approach. It got me through the early days of being out of shape but it's created a habit.

So, I tell myself to "slow your roll" - especially on hot days. If it's a day hike, there's no rush to finish. If it's an overnight, there's no rush to finish. If I am going for several days, there's no rush to finish. 

Not only do I not overheat but I see more of the wonderful nature I am in LOL

Like you @nathanu I use electrolytes in my water (I like the Liquid IV powders) to stay hydrated. 

This will sounds weird, but I had to get comfortable wearing shorts. Not for any vanity reason but just as a way to help avoid bugs. Yeah, yeah, I am out in nature where bugs live... But once I got over the ick factor of bugs crawling on me, shorts made a huge difference. 

Last thing I've learned - sock liners are essential. They wick moisture away from my feet and my socks then deal with it. IT's funny, you'd think wearing extra layers in hot weather would make things worse but my feet feel a lot better and drier when i wear liners.

“Between every two pine trees there is a door leading to a new way of life.” (John Muir)

Superusers do not speak on behalf of REI and may have received
one or more gifts or other benefits from the co-op.

As I write this, I am sipping nuun enhanced water - it is kind of warm outside.  You comments about listening to your body, etc are quite appropriate.

I would add - adjust your schedule.  Be an early riser and get going pre dawn.  You have until about 9 AM  before it really heats up.  In our SW deserts, it is often surprisingly chilly early in the morning - and delightful!!.  There is a reason for midday siestas, with resumption of work toward evening.

if it is really hot, do all your hiking and heavy work after the sun sets.

I favor a cotton full brim hat, dripping wet, and renewed as often as possible.  Wetting you shirt works as well.

When it is really hot, I can easily drink a gallon a day, besides liquid in fruits, etc.  Ration sweat, not water.  Slow down if you have to and learn to recognize the symptoms of dehydration.

Superusers do not speak on behalf of REI and may have received
one or more gifts or other benefits from the co-op.

Lifelong central Floridian here! The heat and humidity are brutal in the summer. We start early, go slowly, and keep hikes, bike rides, etc. short - a five mile hike is plenty in the summer. For hydration, I freeze my water bottles the night before a hike so I have cold water to drink throughout and also to ensure I don’t chug down too much water at once, which has made me sick from over hydration in the past. And when it’s just too miserable to get out, we head to the YMCA pool! 

Oh no!!!heat and humidity!! (he remarked, dryly...)  I am from the American Southwest, where you usually encounter dry heat.  Florida swamps are a different kettle of fish  Soaking your headgear is of much less value.....

Superusers do not speak on behalf of REI and may have received
one or more gifts or other benefits from the co-op.

Hi @nathanu .  I'm in Maryland, and, believe it or not, the humidity here rivals that of Florida.  There are many days that our weather forecasts make that comparison and frequently remark that we are hotter/more humid here than in Florida or Louisiana.  In fact, this last 5 days it has been over 90 F, with dewpoints around 75.      M-U-G-G-Y

In the summer, I wear my buff as a doo-rag (no need to soak it beforehand, sweat will do that in no time).  I wear lightweight breathable and quick-drying shorts, like Outdoor Research Ferrosi, Patagonia Quandary or Eddie Bauer (sorry REI) Guide Pro, and lightweight shirts like Outdoor Research Echo, Patagonia Capilene Cool, or REI Sahara.  I have different, lightweight hiking boots for summer.  I agree completely with @Dad_Aint_Hip about sock liners.  Game Changers!

And, whether I plan on it intentionally or not, the heat and humidity tend to force a slower pace.  I carry extra water in a hydration bladder which I fill with ice.  Not only does that taste better, it acts like a mini air conditioner against my back.  And, since we are blessed with an abundance of waterways, I never miss the opportunity for a quick dip, or at least a wade, through one of them along the trail.

Stay cool out there!

Superusers do not speak on behalf of REI and may have received
one or more gifts or other benefits from the co-op.

Wide-brim hat, long sleeves and pants, all in light colors, and an umbrella you attach to your pack.

Carbs hydrate. Sugar dehydrates. Caffeine/alcohol out.

Grass straw or "Apache Tears" to remind you to keep your mouth shut.

When temperatures go into the 100F's, they put up  signs at Canyonlands National Park trailheads to warn that you will literally die (!) if you try to hike during the heat of the day.   They are not exaggerating, either.   Even though it is actually possible to hike in the early, early morning or by moonlight, no matter how many electrolytes you drink, you still need shade to hunker down during the afternoon. 

 Frankly, when it gets super hot the best plan is, consider doing the hike in a different season when the weather is not an existential threat.    Last year I went on a  desert backpacking trip where  it was so hot we decided to  change our route on the fly from a planned loop hike in order to do an out-and-back in  a canyon with more reliable water.    It can be hard to let go of plans, but even in retrospect I  think it was a truly excellent group decision to be safe instead of trying to tough it out in the heat.

Reading this thread makes me very happy I live further north.  I need shorts sometimes when it is snowing, so I think a southern summer would kill me (or possibly Maryland it would appear)!

Superusers do not speak on behalf of REI and may have received
one or more gifts or other benefits from the co-op.

I grew up on a blacktop crew, literally. I have been outside since in the University of Science Music and Culture, and as a lineman.

Drink before you are thirsty. If your pee is orange, its way past time. Leave the ice at the poles. Cool yes if you can, not cold. Ice water makes you thirsty, can give you a headache and mess up your guts and shock your system. Sports drinks as a supplement, not the primary liquid. Coffee is actually OK. You do NOT get rid of more than you take in, that is a fallacy. You only go more because you drank more.

Hats that breathe, sunglasses, sunscreen. I use SPF Scottish (100). Quick dry light color pants. Light color T shirts.