A great mixture of plants is my usual answer and before you ask - no you can't have specific one's in there :)
The whole idea of the mixed boxes is that you, the customer, get a great selection of plants that are typically fast growing and will take readily in your aquarium. We know how daunting it can be if you are new to plants about which one's to choose, will they look right, do I have the right quantities etc etc. So the hard work is all done.
Now if you want specific plants which I know you sometimes do, then it's best to buy those separately. But just to make it even more simple, all you need to do is work out the size of your tank and then choose the mixed box of plants to suit. It's as easy as that! Oh and one last thing, don't forget your fertiliser and I recommend Neutro T.