To register online with Pag-IBIG, you'll need a valid ID such as a passport or driver's license, proof of income, and your Tax Identification Number (TIN). Make sure you have your personal details handy, including your contact information and address. It's also a good idea to check the official Pag-IBIG website for any additional requirements specific to your situation. If you're unsure about any documentation, consider reaching out to a Pag-IBIG branch or their customer service for guidance.