Saturday Evenings:  Kapa`a Slack Key Saturdays.  Traditional Hawaiian slack key guitar and `ukulele concerts.  September 7 – Hanalei Slack Key Guitar & `Ukulele; September 14 – For the Birds Slack Key; September 21 – Slack Key Story; September 28 – Heart of Slack Key.  Tickets: $20 ($15 keiki/seniors).  A portion of the proceeds supports Na Keiki `O ka `Aina. Located in the Children of the Land Cultural Center, Kaua`i Village (Safeway/Longs) Center, Kapa`a.  5 to 7 p.m.  For information and…