Here's a list of mine. You'd better check the instructions
in I-539 form.
1. written statement explaining the reasons for the request
2. filled I-539 form
3. filled I-134 form
supporting materials:
- statement from Bank
- job contract, etc
4. copies of all pages of passports
5. copies of I-94 forms
6. copies of Visas
7. application fee of $195
8. return E-tickets
Good luck!