How well do sleeves protect against spilled drinks?
My own experience is that, barring using a bag sealer on the sleeves, sleeving is not going to protect against direct spills nor large spills on a hard surface. On a surface that wicks moisture, an indirect spill will not get in. A direct spill (can knocked over onto cards, for example) will penetrate.

I've seldom double sleeved, and will note that it's a major pain to get done, requires two sizes of sleeves, and makes the cards really feel wrong.

And I've seen a card ruined by a direct spill despite double sleeving - a hockey card, to be specific, which was better material than most game cards.