As often seen in Hollywood movies, a bottle of lube (or oil or anything) is something one would always prepare for masturbation.
I'll spare you the detail, but as a European I'm, um, not quite accustomed to this practice.
A quick search on Wikipedia seems to confirm the claim is notable:
While most males and females both produce varying amounts of their own lubrication, it is often desirable to add extra lubrication. There are specific lubricants which may be used in male masturbation but are not suitable for vaginal or anal use or for use with condoms. Lubricant that is safe for sexual intercourse is also safe for masturbation.
Masturbation cream is specially formulated to enhance male masturbation.
Is it a movie cliche or Americans do use it more often than Europeans?