Each gold nugget = 100 crystal coins, it's better to transfer your 100 crystal coins into a gold nugget because the nugget weighs much less than the 100 crystal coins.
to change the 100 crystal coins into nuggets you have to click with your mouse right click on the 100 cc, and you can change the nugget to 100 cc by doing the same.
it's also buyable from the online shop each 5 GNs cost 5 points.