You can show the letter instead of contract, but the letter should contain all the information such as pay, benefits, job description.
If you are unable to provide pay slips submit tax returns, if your income is above the tax relief /slab amount - for Y 2010-2011 the base amount is INR 180,000 - then you are required to pay tax on part of income which is greater than slab amount. In my opinion restaurant managers earn more than the slab mentions above.