This used to be a feature but they removed it for some reason. If you right click, or double click resources in your hand, it would automatically put 4 of those resources into the trade box. 3 if you have a 3:1 port. And 2 if you have 2:1 port for that resource. This made trades with the bank much faster and easier. This used to be a feature but for some reason it was removed and I think it should absolutely comeback.