Hari Raya and the start of the school year always push us into debt. How can we plan for them?

Plan them as known yearly expenses, not surprises: save a little each month and match the celebration to what you can afford.
Allah commands neither wasting nor being stingy (al-Furqan 25:67), and spending according to one's means (at-Talaq 65:7). Hari Raya is meant for joy and gratitude, not showing off; new clothes, festive cakes and Raya money are not obligations. In practice: list the yearly costs (Raya, school fees, uniforms, books, road tax, insurance) and divide by twelve as a monthly fund; set a limit on Raya money; buy school items early or reuse them; and avoid personal loans or credit cards for celebrations. Involve the children so they understand the budget. If the family is truly struggling, apply for school assistance from the zakat centre or the school. See the household budget.