using System.Collections.Generic;

​

public class Program {

    public static void Main() {

        var list = new List<object> {

            "abc",      // string

            1,          // int

            true        // bool

        };

        var TempData = new Dictionary<string, object>();

        TempData["ID"] = list;

        var data = TempData["ID"];

        var test1 = ((List<object>)data)[0];

    }

}