Kiteboarding equipment and instruction/lessons - available from a third party local operator....more info here
Excess baggage....with either airline.
Any meals other than lunch and breakfast whilst on Aitutaki.
Travel insurance......we strongly advise you to purchase comprehensive travel insurance. Various private companies provide it (Air New Zealand, Southern Cross, QBE, Comprehensive, 1Cover)...... read the policy before you commit....things seem to change without warning! Make sure your insurer explicitly covers kiteboarding/kitesurfing (whatevever they call it).