Easy "City Boy" achievement:
Purchase the City Theme for 50 coins. Go to main menu, then select "Play"
Select "Classic", "Zen", or "Tac Nyan" as the game mode in order to have
the "Change World" button appear. However, do not start the game yet.
While any of the previous modes is selected, select "Change World".
Choose the "City Theme" (purchase it now if needed), then select the
"Thumb" button. Begin game play in any desired mode, except "Nyan Wings".
After the tenth play with this theme "City Boy" will be earned.
Easy "Always Cracked" achievement:
You actually need to collect five red and blue energy drinks.