Repeatedly use the bathroom in Helena's and Nancy's bedroom to hear hidden dialog.
Bees
To get the bees to leave you alone when trying to pick flowers for money, buy the yellow spray item next to the flower seeds at the market. Use it to get all the bees down at the same time.
Chinese box code
Go to the chinese box and enter:
Water (in Chinese) - Do this one last
Wood (in Chinese) - Do this one first
Fire(in Chinese) - Do this one third
Mountain (in Chinese) - Do this one second
Code for fax machine
291#*991*7012110026999*#91
Egg
Go to the door to the left of Colin. Pick the lock using the hairpin from Nancy's bag in your closet to get an egg. This will unlock some extras at the end of the game.
There are 9 different rooms in the warehouse, and the lasers are scattered in these different places. Find each laser and you'll find one of those random clicking puzzles, if you know what I mean. Once you deactivate all the lasers you'll be able to get the sapphire.
Italian flag
Go to the marketplace. Create a gelato scoop (in order) consisting of red (cherry), white (coconut), and green (lime) at the gelatin stand to get an Italian flag. This will unlock some extras at the end of the game.
Magazines
The magazines and book stand at the plaza where you will be sent to activate your account has two magazines. One will explain how to pick a lock. The other mentions your suspect's code names, but you will need the German dictionary to read it, as well as the post cards your roommate has laying around.
Bathroom talk...