You need to collect 640 cereal bowls to unlock this achievement.
It unlocks as soon as the in game counter at the top left of the screen reaches the required amount.
The easiest way I've found is to start a new game and progress past the first boss. This will net you over a hundred bowls. Then, play the level after the first boss as follows:
Run right. Collect the bowls. Jump across the three birds, collecting another 12. Run right again to collect more, jump through the air to collect even more, then fall in the chasm which will retain the number of bowls collected and start you back at the beginning of the level within a couple of seconds.
I went from just over a hundred to over 650 within ten to fifteen minutes or so. Make sure you collect at least 650 to unlock the five related achievements!
Easy peasy!