I have gone through this ordeal of surrendering registration in the case of one of my clients and the documents which you need to submit are as follows:
1 Copies of all ST3 Returns since your registration along with the copy of payment challans
2. Original copy of the Registration Certificate
3. Undertaking as mentioned by Learned Pradeep Kahtriji
4. They asked for balance sheets and Income tax return copies also in the first place which after some deliberations they dropped.
5. Again when you do the surrender process through the system in ACES please be careful to take a print out of the Surrender form as this form does not get stored in the system and cannot be retreived. I faced this problem and had to get copy from the Department