Ideas --
One -- get a great Chinese meal in Richmond. Anywhere along the Canada Line. Dim sum or something else, depending on what you like and the time of day. Richmond is extra special, and authentic for this.
Two -- there is of course the new outlet shopping mall on the Canada line, at Templeton, called McArthurglen Outlets, a few minutes from the airport. Just wander don't shop, it is supposed to be done quite nicely (I have not seen it yet as I too, don't shop). Supposed to be a decent people watching place. I think it connects to a walking path / bike path out here, and can be a nice nature walk, too.. You could take the train here, then walk back to the airport if you have time along the bike path which is along the road,but separated, with landscaping.
Three -- just take the Canada Line to Marine drive and back again -- the mountain views are good until you go underground.
Four -- take a taxi to Iona Beach park, or MacDonald beach park, both a few minutes from the airport, on SeaIsland (where the airport is) Walk around.. enjoy being at the sea or next to the fraser river....
Also
Casino -- River Rock at bridgeport station..? Not for me, but maybe you?