LSD doesn't make you see things (or people, etc) that aren't there; it magnifies (intensifies or electrifies) what (or who) IS there.
When Don and Megan are in the car, Megan asks Don to roll down his window when he starts smoking. Even though he makes the motion of cranking the lever, the reflection of his suit can be seen all the way to the top of the completely closed window, even on the close-up. However, Don cranks open the wing window, not the main window, therefore this is not a goof.
During his LSD trip, Roger "sees" a Model A Ford in the parking lot of the 1919 World Series. The Model A was the successor to the original Model T and wasn't introduced until 1927. However, Roger was hallucinating under the influence of LSD and would have "seen" any number of things not correct for the period.
When Roger and Jane drop acid at Jane's psychiatrist's apartment, Roger uncaps a bottle of Stolichnaya vodka. Stolichnaya, distilled in then Soviet Russia, was unavailable in the west until a 1972 deal with Pepsi to distribute the vodka in the U.S. and the soda in Russia.