A colon must follow an independent clause. 'I need' or 'I need to buy' are not independent if 'the following' is missing in some contexts, but 'The items I need to buy are' is also weak. The most formal and correct structure uses an explicit introduction like 'the following'.
A colon must follow an independent clause. 'I need' or 'I need to buy' are not independent if 'the following' is missing in some contexts, but 'The items I need to buy are' is also weak. The most formal and correct structure uses an explicit introduction like 'the following'.