There are ways to fill small holes in walls without buying plaster. This guide is about homemade spackle.
This is old but good. Back, way back in college dorm life, at the end of the year they would charge us if there were holes in the wall or marks etc. My room mate would take out the spearmint green tooth paste and fill all the holes to clean up any holes. Worked great and we were never charged a cent.
Source: my old room mate, Anne
By Brenda from Charlotte, NC