Whoa! These green coconuts contain only 'coconut water'. At this stage none of the coconut meat has started fo form on the inside of the shell. They're called 'dirinking nuts' at this stage.
Once opened, drink it straight away, or within a few hours. It doesn't keep till next day, and doesn't refrigerate well.
Heathfield is right, they're drinking coconuts. The coconut water inside is very nutritious.
Apparently back in the Caribbean, the people drink it regularly!
Goodsoulette is talking about what's called a 'jelly nut' rather than the 'drinking nut'. When the coconut meat begins to form on the inside of the shell it's a thin clear jelly-like substance. This gradually turns white as it increases in thickness and becomes firmer. When it's about 3 to 5 mm thick, it can be scooped or peeled off the inside of the opened nut and eaten. Delicious! Quite filling, and with a very 'coconutty' taste.