PORT is a red wine, and red is the left side of politics. Red Left Port. There's always some red port (wine) left.

Mnemonic Device

• PORT is a red wine, and red is the LEFT side of politics.
• Red Left Port.
• There's always some Red Port (wine) Left.

Explanation

to remember the name of the vessel's left side, and the light color on the port side.

Additional Note

PORT and LEFT both have four letters.