Don't pay too attention to the previous answers.... I've got this one!
I've had a severe crushed ice addiction for about 5 years and I've figured out a few ways to help keep crushed ice fluffy and dry. And believe me when i say I've tried damn near everything.
First and foremost, you MUST blend/crush the ice in a FROZEN BLENDER! (keep in freezer for at least 2 hours prior to crushing the ice (I keep my blender in there 24/7 because crush at whole lot, and often).
2nd, when blending don't waste anymore than 45-60 seconds getting ice into blender, crushing it then back into the freezer.
Most importantly, make sure the container you store any crushed ice in is FROZEN solid... I have found that a stainless steel bowl is very good at helping the fluffy and dry cause....
And....lthough you don't have to the following, it does make a huge difference if you don't have a sub zero freezer... and that's putting a couple of blocks of DRY ICE in the freezer near/under your crushed ice.
(Do a Google search and find a local dry ice supplier and get a click or two the day of your party).
I keep a metal potato masher in the freezer. .I use it to mash up the ice if it isn't totally fluffy and dry.
*Bonus Tip for carrying fluffy ice in a personal/small cooler...
The night before put whatever size cup(s) you're going to be transporting inside the cooler and fill it with regular ice, then put the whole cooler in the freezer....the next morning when you remove frozen cups you'll have a perfectly 'fitted' spot for the cup you're gonna carry/transport.
Fill your cup(s) with your crushed ice and immediately put it/them back into the freezer until you're ready to walk out the door. When you're ready, get the cooler out, and ADD SALT! And i don't mean a pinch... I'm talking like a 1/4-1/2 cup per 5 pounds of ice. Salt decreases the temperature of ice significantly and I guarantee, if you use an aluminum cup/mug for your crushed ice and put it immediately into the empty space in the cooler (where those empty cups were) and cover it/close the lid, you'll have 8 straight hours before that fluffy ice begins to melt.
I know.....I know, it's actually pretty damn sad that I know this shit.
BTW, a sub zero freezer is your best bet.