The scene with all the boys on the cover of the porno magazines coming to life and interacting was not done with any computers. At the time of production, CGI was still a very expensive tool. The individual pieces were filmed with the actors standing behind large pieces of plexi-glass, with the mock-magazine cover on front. Later, optical effects, similar to those used in matte painting, were used to composite them together on the "magazine rack".
The image of the falling barn was something Gus Van Sant used to paint for years. He said it represented leaving home and knowing you'll never be able to return.
Gus Van Sant gave copies of John Rechy's novel "City Of Night" to River Phoenix and Keanu Reeves to help get them into the mindset of street hustlers. Keanu found the book very useful, and went on to read five other Rechy novels. River reportedly stopped reading after the first paragraph. "He had his own background to draw on," Gus Van Sant later said. "I think River had an entire youth spent traveling with his family, no connections to society, no roots, no permanence. He crafted that character himself."
In late 1990, Keanu Reeves rode his motorcycle from Canada to Gainesville, Florida, to hand-deliver a copy of the script to River Phoenix because Phoenix's agent refused to show Phoenix the script.
Many members of the cast (including River Phoenix, Keanu Reeves, Flea, and Michael Parker) moved into director Gus Van Sant's large old house in Portland, Oregon during filming. They apparently caused such a disturbance (staying up late, getting drunk, partying, and playing music) and overtook the house to such an extent, that Van Sant eventually had to move out of his own house and stay with a friend, in order to get some sleep.