Bank statements. Income letter from employer. Letter from employer verifying that you will have a job waiting for you when you return, etc.
PROFESSOR OF IMMIGRATION LAW for over 10 years -- This blog posting is offered for informational purposes only. It does not constitute an attorney-client relationship. Also, keep in mind that this is an INTERNET BLOG. You should not rely on anything you read here to make decisions which impact on your life. Meet with an attorney, via Skype, or in person, to obtain competent personal and professional guidance.
letters from bank stating you had the funds in deposit for longer than 6 months, pay stubs, or rent contracts showing your sources of income and amounts.
You may submit copies of pay stubs, recent bank statements, recent tax returns, proof of employment, letter from your bank, among other things. If you are concerned about whether you have sufficient evidence, you can hire an immigration attorney in the U.S. to review what you have and make suggestions. Most of this can be done electronically. All the best.