Most surfers bring 2-3 boards for a 10 days boat-trip.
If you are in “good shape” we recommend a quiver between 5’8 and 6’5, depending on your height/weight.
If you don’t surf very often it’s important to bring boards with good floatation (volumes over 28 litters, or even more if you are a heavy guy) so that you catch the waves early without being late at the take-off or going over-the-falls.
If you ride a longboard bring it along, but consider bringing also a shorter board (retro, fish, malibu) as sometimes longboards are not easy to handle in some of Sumatra’s hollow waves.