St Lucia helicopter transfer-luggage question

Considering helicopter versus ferry transfer. Traveling w/ carry-on only. Helicopter website says standard carry-on suitcase and small personal item allowed. Does anyone know the size of ‘personal item’ allowed? As in your standard personal item on a plane, or smaller? I would hate to take the chopper And have them say my personal item is too large and then they want to take our luggage via Van. TIA