The receiver - requires only a battery, photoresistor, and audio jack.
Using a simple laser pen pointer, a few misc parts, and about 15 minutes, you can make a simple laser communicator that converts a sound source into light that travels across a room, and back into sound with very little quality loss.
To make this more fun, you need to extend the range - which means a stronger laser. You could use a pre-made laser module with proper colimating lenses already included, but for the ultimate in range and fun, I would think a frequency-modulated VCSEL transmitting digitally encoded audio pumped out with high currents pulses at an extremely fast bit-rate would give you an ultra narrow beam laser walkie-talkie with many hundreds of feet range that would be very difficult to detect and even harder to snoop on. (And that's before you even start playing crypto games with the transmitted data.)
(If you're interested in more about laser diodes, check out the laser diodes/diode lasers section of the sci.electronics repair FAQ.)