Unity editor menu item for creating MonoBehaviour subclass. Place this file into 'Editor' folder.

CreateMonoBehaviourSubclassMenuItem.cs

using UnityEditor;
using System.CodeDom;
using System.IO;
using System.CodeDom.Compiler;

public class CreateMonoBehaviourSubclassMenuItem {
	[MenuItem("Assets/Create/File/MonoBehaviour Subclass...", false, 11)]
	private static void CreateMonoBehaviourClass() {
		var filePath = EditorUtility.SaveFilePanelInProject("Save file", "MonoBehaviourSubclass", "cs", "Enter class name");
		if (!string.IsNullOrEmpty(filePath)) {
			using (var streamWriter = new StreamWriter(File.Create(filePath))) {
				using (var tw = new IndentedTextWriter(streamWriter, "    ")) {
					var fileName = Path.GetFileNameWithoutExtension(filePath);
					var unit = BuildMonoBehaviourSubclassGraph(fileName);
					var provider = CodeDomProvider.CreateProvider("CSharp");
					provider.GenerateCodeFromCompileUnit(unit, tw, new CodeGeneratorOptions());
				}
			}
		}
		AssetDatabase.Refresh();
	}

	private static CodeCompileUnit BuildMonoBehaviourSubclassGraph(string className) {
		var unit = new CodeCompileUnit();

		var @namespace = new CodeNamespace();
		unit.Namespaces.Add(@namespace);

		@namespace.Imports.AddRange(new [] {
			new CodeNamespaceImport("UnityEngine"),
			new CodeNamespaceImport("System.Collections")
		});

		var declaration = new CodeTypeDeclaration { Name = className };
		@namespace.Types.Add(declaration);

		declaration.BaseTypes.Add(new CodeTypeReference { BaseType = "MonoBehaviour" });

		declaration.Members.Add(new CodeMemberField {
			Name = "_transform",
			Type = new CodeTypeReference("Transform")
		});

		var methodAwake = new CodeMemberMethod { Name = "Awake" };
		methodAwake.Statements.Add(new CodeSnippetStatement("\t\t_transform = GetComponent<Transform>();"));

		declaration.Members.AddRange(new [] {
			methodAwake,
			new CodeMemberMethod { Name = "OnEnable" },
			new CodeMemberMethod { Name = "Start" },
			new CodeMemberMethod { Name = "Update" },
			new CodeMemberMethod { Name = "FixedUpdate" },
			new CodeMemberMethod { Name = "OnDisable" }
		});

		return unit;
	}
}