You'll need 1 gallon and 1 quart Silmar 249B resin to glass a 9'0 longboard. You'll also need 2 oz MEKP catalyst and 2 oz Surfacing Wax (for hotcoating). If you plan to gloss and polish the board as well you will need an additional quart of Silmar 249B resin and 2 oz Styrene to add into the resin for glossing.
Here is a chart for how much resin to use for each step in the glassing process: