I797 and client letter is must.
Besides that you can take everything with you. Here is the list:
Documents an H1-B applicant needs to carry for Visa interview:
1. Passport and Passport copies of all pages
2. DS-160 confirmation page (Barcode printout)
3. Original Visa interview appointment letter
4. Employer agreement / Employment contract letter signed by you and Employer Company (Original) / Contract between candidate and petitioner
5. Offer letter from the current Employer
6. Pay stubs for the last 2 years
7. Experience letter from the previous jobs
8. Employer letter/ Employment Verification Letter
9. Client Letter – Make sure Client mention Petitioner’s name in the Letter
10. W2’s and Tax Returns (for the entire period of your stay in USA)
11. Bank statements for last 2 years highlighting Direct deposits
12. Updated Resume
13. I 20's (All Original)
14. OPT Cards
15. Work location pictures (not necessary)
16. Client ID/Badge, Employer ID/Badge
17. Time-sheets/status reports
18. Client location photos (optional) (not necessary)
19. Two passport size photographs as per specification
20. Work Experience Certificates, reference letters, appreciation certificates from previous or currentemployer/s (from the start of your career)
21. All Original Academic Credentials along with mark sheets(MS, BTECH, INTER, 10th)
22. SSN card
23. Driver’s license
24. H1B data collection and filing fee exemption supplement
25. H classification supplement to form I129
26. H1B visa petition and supporting docs filed with USCIS
27. I-797 – Original
28. I-129 &H1B cover letter
29. Copy of LCA
30. Previous I-797A and LCA (If any)