As per the usual schedule, employers issue Form 16 around mid-June, i.e before June 15. For FY 2023-24 (assessment year 2024-25), Form 16 should be issued by June 15, 2024.
You would need Form 16, house rent receipt (if applicable), investment payment premium receipts (if applicable). However, ITRs are annexure-less forms, so you are not required to attach any document
ITR-1 can be filed by an individual having income up to Rs 50 lakh and who receives income from salary, one house property and other sources (interest, etc)