SD and micro-SD drives
SD and micro-SD cards have can have memory space up to 128 Gb, are inexpensive and very small. They fit in most phones and are easy to load with data and distribute.
Bluetooth allows device to device distribution (phone to phone, computer to phone, phone to computer etc).
Devices such as LightStream, AirStash, Library Box, Pirate Box or Raspberry Pi allow transfer of files through a local wifi network.