As with servers or any other equipment, I recommend that you use pouch folders to store all documentation, CDs, DVDs, warranty info, etc. You should also have customized checklists for each client - and update them with each machine you deliver.
Here's my latest SOP video on this subject:
Just remember: That machine build checklist probably has some secure information on it - so be sure to treat those printouts with respect and keep them safe.
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Also see the earlier videos on server documentation.
Documenting a Server, Part 1
Documenting a New Server, Part 2
Documenting a New Server, Part 3