If you see the check list, it is clearly given what to send.
Anyways, it should be an experience letter, on official letter head, showing your duties in detail, and time from when to when you have been working, rank, etc etc.
You should also attach proof of being paid, salary slips, official letter from your employee that what is your salary etc etc.
Also attach the contact details of your Immediate boss, visiting card, or a Print out with all of His/Her details, cell number, office contact etc etc.
And if you can, a notarized copy of Contract.