If you use a kingdom card to get goods and still have them left at the end of the turn, the rules say you can place them on your Guild cards as long as you don't exceed the limitations of the guild cards. The only limitation I can find is that you can only store 2x as many cubes as the number on the guild card.
Is it really that simple? Can you add cubes to Guild cards that don't normally produce like Day Laborers, Mercenaries, and Open Space? Can you add cubes to cards that don't produce that good (like adding a Rice cube to a card that produces wood)?
I believe I'm over-thinking this...
The goods can be placed to any cards within limitation for quantity.
For example, the rice cube from the Kingdom card can be placed on the Day Laborers, open space and so on.