An agency needs enough information to decide whether it wants to see more. That usually means current natural images, accurate basic details, your location and a reliable way to contact you. If the agency publishes a form, the form wins over any generic checklist.
Do not turn a first application into an archive dump. A retouched campaign image, fifteen old shoots and a long autobiography can make the useful information harder to find. Send what the agency asks for, then stop.
Keep a record of the date, channel and material you sent. If there is no answer, you can decide later whether a follow-up makes sense without guessing what happened.