Essential: a cot or cot bed with a properly fitted mattress, and somewhere safe to change a nappy (a dedicated unit, or a changing mat on any stable, waist-height surface). Everything else is genuinely optional in the first few months.
Very useful, not essential: a chest of drawers with a changing top, since it saves buying a separate unit, and a comfortable chair for night feeds, which matters more for your own back and shoulders than most people expect going in.
Can usually wait: a wardrobe (baby clothes fit in a chest of drawers for a surprisingly long time), a full matching 3-piece set bought all at once (pieces can be added gradually as budget allows), and most decorative extras.