What about a Sydney Harbour Kayaks Gift Voucher?
The voucher is a nicely presented hard card that can be picked up or mailed out anywhere.
The recipient of your gift has 48 months to redeem and you can choose any amount.
They don't even have to spend it all at once. If you are short of time and the party is in a few hours; then you can safely book it online and the voucher will be instantly emailed.