By default, Resharper does not specify any usings in .cs files. Is it possible to configure it to add one or two usings by default
First of all, you can use a special kind of intellisense called Import symbol (Shift-Alt-Space) instead. It would show you all available methods regardless of their namespace and then it would import everything.
But if you still want additional usings, then in addition to advice from @Hadi Eskandari I can suggest to go to ReSharper | Options -> Code Editing | C# | Namespace imports and add your namespaces to "Namespaces that should always be imported". This way ReSharper would not suggest to remove your namespaces and would always add them during Code Cleanup.