Here's a list you can format and add/subtract to/from:

Domain admin username and password:
Domain registration details and logins:
Domain DNS hosting details:
Domain Web hosting details:
SSL Certificate provider login details:
Local PC usernames & passwords:
(If applicable)
List of Microsoft Servers and roles:
Switch details and logins:
Router details and logins:
NAS details and logins:
Access Point details and logins:
Printer/MFP details and logins:
Web filter proxy (If applicable):
Key IP addresses & usernames / passwords of anything else relevant i.e Office 365, Cloud Services:
Server details (brand, model, serial, warranty):
Virtual Environment details:
UPS details (Logins / warranty):
Antivirus uninstall passwords (all products):
Cable or Fibre details (provider plus account details – login):
Secondary Internet Connection (If applicable):
Offsite backup details eg. Storage, S-Protect licences, cloud services:
Wireless Network SSID / Password:
Service Account Usernames and Passwords eg. Backup printers:
iLO / iDRAC login / password:
Remote access methods:
Phone System:

MS Licence Agreements / Login:
Antivirus / malware / Spam – product, login and expiry:
Firewall – Model / Serial / Licence expiry and supplier:
Virtualisation agreements (VMWare / Hyper-V):

Software Management
Provide details on all business applications:
SharePoint (If applicable):

Documents to be provided
Router / firewall details:
Switch / Router Configuration Files:
Any VPN Config – pre shared secrets / config:
System Documentation including diagrams:

Outstanding Problems or Project work to discuss
Current issues, tips on support / maintenance, etc:
Active / unfinished projects:
Support contract expiry date:
Pre-paid support hours in credit: