- as follows:
[1] the chest is predetermined before you click what you will get next.
[2] chips are determined by level and not by color
[3] cards are determined by group and not what particular hero (purple, gold or leader)
[4] if you do not have a map piece in your possession then you can get a map piece (you are not holding a map piece while sailing, its a complete map at that point). if you are holding a map piece then you will get coins according to your level instead.
that being said, by opening and closing your chest instead of clicking shuffle you can rule out by elimination process what kind of reward you are getting. then when you determined that you will get for example a level 2 chip, you can choose the color of the chip by opening and closing the chest until you have the color you want. the same for the purple and gold heroes.
tip: if you are supposed to get a map piece and don't want one then get a map from assistant, guild claim or steal/sink from someone. when you return to your guild chest you will now find coins instead of the map piece.
good luck and have fun