I'm sure someone will be able to provide you with specifics, but go into your upgrade menu and down to the inorganic materials. Anything that gives you like 800 or more points you should hang onto, the rest of the inorganics you can afford to sell.

You shouldn't really need too much in the way of gil so you could just as well hold onto everything like I did. Upgrading gets easier at the end when you can buy kickass materials to manipulate everything in your favour.