public interface IRandom
{
             float itemDropChance
             {
                 get;
                 set;
             }
}

public class ItemLoot : IRandom{

public static List<ItemLoot> AllItems = new List<ItemLoot>();

string _nameID;
float  _itemDropChance;

public string nameID{
get {return _nameID;}
set {_nameID=value;}
}

public float itemDropChance{
get {return _itemDropChance;}
set {_itemDropChance = value;}
}

public ItemLoot(string nameID, float itemDropChance){
this.nameID = nameID;
this.itemDropChance = itemDropChance;
AllItems.Add(this);
}

}

public class GameEventSpec : IRandom{

public static List<GameEventSpec> AllItems = new List<GameEventSpec>();

string _nameID;
float  _itemDropChance;

public string nameID{
get {return _nameID;}
set {_nameID=value;}
}

public float itemDropChance{
get {return _itemDropChance;}
set {_itemDropChance = value;}
}

public GameEventSpec (string nameID, float itemDropChance){
this.nameID = nameID;
this.itemDropChance = itemDropChance;
AllItems.Add(this);
}

}

public static class ExtensionMethods
             {

}

public static T ReturnRandom<T>(this List<T> items) where T : IRandom
             {
                 System.Random _r = new System.Random();
                 List<float> probs = new List<float>();
                 float total = 0f;
                 for (int i = 0; i < items.Count; i++)
                 {
                     probs.Add(items[i].itemDropChance);
                     total += items[i].itemDropChance;
                 }

                 int index =  probs.Count - 1;

                 float RandomPoint = (float)_r.NextDouble() * total;
                         
                 for (int i = 0; i < probs.Count; i++)
                 {
                     if (RandomPoint < probs[i])
                     {
                         index = i;
                         break;

                     }
                     else
                         RandomPoint -= probs[i];
                 }

                 return items[index];

             }

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class Testing : MonoBehaviour{

void Start(){

new ItemLoot ("Apple",25f);
new ItemLoot ("Gun",15f);
new ItemLoot ("Sword",125f);
new ItemLoot ("Bomb",55f);

new GameEventSpec("Darkness", 50f);
new GameEventSpec("Hot", 25f);
new GameEventSpec("Cold", 10f);
new GameEventSpec("Wet", 30f);

          ItemLoot ItemLootSelected = ItemLoot.AllItems.ReturnRandom<ItemLoot >();
Debug.Log(ItemLootSelected.nameID);

GameEventSpec GameEventSelected = GameEventSpec.AllItems.ReturnRandom<GameEventSpec >();
Debug.Log(GameEventSelected.nameID);
}

}