Yeah, there'll likely be a fair amount of posts on this one.

The real issue, at least in July & August, is getting the drink cold. Best I've been able to do is fill a nalgene with water, put it in a net bag weighted with rocks, and get it as deep as I can for about 30 minutes. I can't say the water is truly cold, but it is better than what you can get at the surface. It's also a lot of work, and you still have to drink it before it gets warm again.
My personal preference is Bombay Blue Sapphire gin with Crystal Light iced tea. I call 'em t-bombs.
I once heard from a guy in Ely (in Cranberry's over a beer) about a guy who used the same technique to sink a 6-pack of beer somewhere between Moose lake and PP, then concealed and tied off the line along the bank somewhere. Days later, on the way out, he would retrieve the libation on the way back to Moose Lake and enjoy a cold one as he paddled in. I'm a little skeptical on this one, but stranger things have happened I guess.
By the way, booze is really cheap at the duty-free shop when I cross the border.
regards,
Wind-in-Face