The RFE document clearly states how to response that. It contains an envelope, a RFE coversheet (blue color) and one/two page(s) of description what are the documents they are asking for. Just attach those documents they have asked for with the blue coversheet and send it back in the envelope they provided.
Keep a photocopy of blue coversheet with you. And also write down the address on envelope.
Do not send response by first class mail. Either send it by certified post or by FedEx.
Medical, I guess, you know what to do.
For proof of legal status (assuming it asked for your current status (not past):
1. Your current I-94 (both sides)
2. If you currently working on H1/L1 send a copy of visa stamp on your passport. Also H1 approval notice (Notice of Action).
3. If you are working on EAD, send a copy of your EAD card.
