Using a DVD with 4.7GB of random bits or random characters from /dev/urandom is probably good enough for most people for a time frame of 5 years worth of communications. People with a necessity for a longer time frame could do this with 10 TB hard disks and have private bi directional or (group based ) conversations with trusted parties for several years like maybe 20 years as long as you don't start sending large files. It should be good for text, pictures, audio and small video clips.
For more serious people getting actual random numbers will be a priority, by building some kind of physical or electronic device that can generate random static to record to disc. A Geiger counter, radio transmissions on a static channel. Maybe take all of these inputs and sum them together and add it to the output from /dev/urandom.