You can, but i wouldn't call it easy.
You can import tables and get the data and field definitions in one import--use the new table option.
You can copy and paste all the objects in a layout in one copy/paste operation.
You can import scripts
But, there are other parts of the process that can't be imported or copy/pasted:
Non-custom value value lists
Table occurrences and the relationships that link them to other table occurrences.
Also, since scripts can refer to layouts and layout objects and layouts can refer to scripts, you have to do it all in just the right order to avoid getting a layout with numerous buttons and script triggers that need to be "reconnected" before they work.
There is a 3rd party utility called FMMigrator--that is supposed to make this much easier to do. I haven't used it myself, but I'd definitely investigate it if I had another large "file merge" project at hand.