Here I will put a list of “must have” libraries in most of your .NET (Core) projects:

• Autofac – dependency injection replaced with embedded DI/IoC – typically it is enough
• Entity Framework Core – access to SQL database
• RestSharp – HTTP client (if you have to send requests to other URIs)
• Serilog – logger
• Application Insights – complex logging & log presentation (or equivalent if your app is deployed in the cloud)
• Security Code Scan – security scanner (more in this post)
• Scrutor – add Decorator injection to Microsoft’s DI in .NET Core

Testing:

• xUnit
• Moq – mocks for unit tests
• FluentAssertions

Other tools worth to consider:

• Choco package manager for Windows (https://chocolatey.org/)
• OWASP Dependency Check – tool to detect known vulnerabilities in dependencies (e.g. nuget packages); can be used as plugin in build server