a resident of a coastal area
"As a true coaster, she spent her summers fishing in the bay rather than working an office job inland."
someone who coasts
"After years of hard work climbing the corporate ladder, he became a true coaster when his company decided to lay him off during the recession."
a covering (plate or mat) that protects the surface of a table (i.e., from the condensation on a cold glass or bottle)
"Please pass me a coaster before you set your iced coffee down, otherwise it will leave rings on my wood table."
Agent noun of coast: one who coasts.
"The new electric bike is perfect for anyone looking to be a true coaster down the mountain without pedaling."