1L of tea
The second hot day after traveling back from Japan, I bought 1 big cup of tea from this tea shop 囍茶 in my neighborhood.
It's one litter of ice tea with an iPod Touch:
And now with the Macbook Air:
It costs only 20 NTD (0.6 USD / 56 JPY), it makes the Macbook Air looks much smaller, and it cools me, and the whole room down.