The central, unexpanded, leaf bud (called rito) at the top of the tree was very popular with Maori as food, either raw or cooked, unfortunately it does kill the tree, which is why early settlers called it millionaire's salad. Young flower buds were also eaten. The leaves were used to wrap food prior to cooking in a hangi.
Both the sap and the pith of the nikau fruit was used in pregnancy related conditions. When eaten, the pith gives a slightly laxative effect, and in pregnant women this helps relax the pelvic muscles. The sap was consumed to ease labour during child birth.
The old time Maori used nikau leaves as thatching for the roof and walls of the whare (house). A whare build with a manuka stick framework and nikau thatching is supposedly as strong and watertight as if made of iron. The leaves were also woven into baskets and kits. Nikau leaves still make good thatching for bush shelters and the padding in a camp mattress.