Maintaining his Neverland Ranch was certainly a huge financial drain for him because it required a lot of money annually (such as, staff payments, energy bills, insurance, etc).
Michael Jackson also used to indulge in shopping therapy (i.e., to shop in order to make himself feel better and more cheerful).
Keep in mind that he also used to spend a lot of money on numerous cosmetic plastic surgeries/procedures.
Forensic accounting expert William R. Ackerman also testified (during the 2013 trial) that Michael Jackson used to spend a lot of money on expensive gifts, expensive art items, expensive cars, expensive jewellery and expensive furniture.
William R. Ackerman also pointed out that the singer used to donate huge amounts of money to numerous charitable organizations.
Note also that given his huge debt when he was alive, the cost of that debt was also huge (meaning, he had to pay annually a lot of money also on the interest of that debt).
It has been estimated that Michael Jackson overall had to pay 30 million US dollars in annual payments on his debt.