Truly, we tried the mister water bottle. Getting wet actually made us MORE sticky and miserable, not more comfortable. Think about it, which feels better - a dry summer day or a humid sticky day? What you wnat to do is to try and stay as DRY as possible. Use deoderant.

A mister makes it feel MORE humid.
Also, see which side of socks thing works for you - do your feet stay more dry with socks or without? If you go with socks, try to find ones that are geared towrds summer wear. Investing is a pair of runners socks will not be wasted money. (the kind with ventilation panels, usually the same price as any other socks). I usually prefer sock free, but DH usually prefers socks.
Similarly, to stay dry and fresh, we found it helpful to change for dinner some days. I dunno about you, but I really don't want to arrive at a place like Cali Grill wearing sweaty t-shirts. If you will be having TS dinners, it may pay to bring a change of clothes. the trick for us is to find clothes that look 'nice' but are comfortable enough for the parks. Like I'd never wear uncomfortable shoes at WDW, but attractive AND comfy shoes are a hard find.
Seaking of shoes, in summer we all like a pair of good quality sandals. Ecco meaks some nice ones, Keen and Teva are also some good bets. You want shoes that can get soaking WET!!!!!!
Crocs are another option, especially for Kids. Your feet are alwyas essentail at WDw, so avoid cheap flip flops, worn out shoes, etc.
DO plan on heavy downpours. they ownt last all day, but you will likely get some. You can better prep as your days get very close and you see a weather prediction. Likely a few $.99 plastic ponchos and a rain jacket are smart to bring. If the prediction of rain is 50% or less - bring the poncho. If rain is above 60% odds, bring the rain jacket for the day. that means you need a means of carrying a jacket for those days. Agian, you dont need to get all that now, just once your dates get close.
Never used, wanted a neck cooler thing. We did use our swimsuits?
I do like botteld water. If you have s troller, you can stow them there. Otherwise, you can simply refil your water bottle. At every meal, we ask for a cup of free ice water. Once in a while, we DO our the meal water into our bottles. Dehydration sickness will ruin your vacation.
I further disagree with talc. It blocks your pores, which makes you more miserable. Not only that, but it cakes up. Yuck! It is much better to keep your skin as free and clear as possible.
Another thing I'd suggest is to acclimate yourself to being outdoors before you go as much as you can. I alsyws advise folks to go for 30min walks each day before they go to WDW.
Truly, we enjoyed our summer visits very much!