During your stay you can just join the Mentawai and eat what they eat. The staple diet consists of sago, complemented with roots and whatever is available from the forest and small food gardens. This diet is not for everybody though, particularly not when staying longer than 1 or 2 days.
Upon request your Mentawai hosts can prepare other meals, including rice, noodles, vegetables, canned fish, eggs, pancakes, etc.
You can either buy food supplies yourself upon arrival in the harbor of Siberut, or have your hosts do the shopping in advance.
We highly recommend this option, to complement the traditional Mentawai you will be offered. You just pay for the shopping and a fee for the cooks.