There are a couple of ways this could be done:

• USB memory stick - copy the files from one Pi on to the stick, and then move them to the other.
• Network transfer - via a protocol such as FTP, SFTP. The Pi's have to be connected to the same network (e.g. via wireless USB adapters), you will also need their IP addresses and a server running on at least one of them
• Serial - there are two serial Pins on each Pi's GPIO, you should be able to connect them to get a basic serial connection:

^Source

You could then emulate a network connection over that.

There are a couple of ways this could be done:

• USB drive - copy the files from one Pi on to the drive, and then move them to the other.
• Network transfer - via a protocol such as FTP, SFTP. The Pi's have to be connected to the same network (e.g. via wireless USB adapters), you will also need their IP addresses and a server running on at least one of them
• Serial - there are two serial Pins on each Pi's GPIO, you should be able to connect them to get a basic serial connection:

^Source

You could then emulate a network connection over that.