I haven't been that time of year, because much as I love the heat .... ouch! 31 /32 degrees, can be hotter and with the humidity can be very uncomfortable . Very humid. If you are that attractive to things that bite DEET is a must - but you MUST use biodegradeable sunscreens. Make sure you have high factor or sunblock - you will need it. Rain ponchos - this is the start of the hurricane season, and although they seldom land in this area, expect some rain, and if you are unlucky, torrential rain albeit short lived. More often short sharp showers, usually early evening or late afternoon. But if there happens to be a storm - go out in it. They are often spectacular, fun, and you'll dry off within minutes (as much as you will ever be dry anyway) after it finishes.
I haven't ever used humidity pouches. Never had a need for them.
Check all your vaccinations are up to date. Malaria isn't common but Zika and Dengue are present and there have been cases of Chikungunya. Make sure you recognise the symptoms, just in case you are unlucky.
It's very safe in the main - make sure you have a cross body bag though, and keep valuables to a minimum. Never carry all your cards at once - make sure you have some in the hotel safe.
Most of the places are not easily walkable - it's a big area - but there are loads of tours for sale, so shop around. If you want to drive, I would personally hire a car and driver rather than self-drive. Easier all round and usually affordable if you haggle a bit.
Do go to Xcaret and stay for the day/evening show. Obviously there's archaelogy to die for BUT there are still a few sites (or there were when I was last there) where they allow tourists to climb them - do not do this! You are helping to damage ancient history to a point where it cannot be repaired or retained, and even if others do it, that doesn't excuse knowing the damage it does and doing it anyway.
Ask if there is anything I have missed off that you want to know about. Oh and before I forget - either large hand fans or rechargeable ones (usually have both on hand). A cooling breeze can be essential at times. And I'd advise, especially if going out, adopt Mexican time - start early, afternoon siesta in the shade, then party on! The heat can be draining and dangerous at times.
Some of that sounds scary, but it's not - just be sensible and you will have a great time.