How do you choose a good one?
There are two kinds of coconuts available at the store: brown ones and white ones. Brown, mature coconuts have a rough, stringy husk, the thickest, firmest meat, and the least amount of water. This type is best for eating or turning into coconut milk and oil. White coconuts are young, bigger, smoother, and carved into dreidel-like shapes. They have soft, delicate flesh and lots of sweet water. These are best for drinking.
Whichever kind you're buying, pick the largest and heaviest because that indicates there's lots of juice. Check for cracks and mold spots, then shake it. You want to hear that water sloshing around! If you don't, that means it's old. For the freshest selection, shop at Mexican or Asian markets -- they have a faster turnover for coconuts than American supermarkets do.