ItemStack.cs

using UnityEngine;
using System.Collections;

public class ItemStack {

    public Item ContainingItem; // The item that the itemstack is holding.
    public int StackSize = 0;
    public int MaxStackSize = 1;

    public ItemStack(Item i, int s /* <-- Stack size */) {
        ContainingItem = i;
        StackSize = s;
        MaxStackSize = ContainingItem.MaxStackSize;
    }

}