Alright, I've got 20 minutes to kill...

public class Inventory
{
    List<InventoryItem> items = new List<InventoryItem>();
    InventoryItem selectedItem;
    Player owner;
    int currentlySelected = 0;
    public void Init(Player newPlayer)
    {
         newPlayer = owner;
    }
    public bool AddItem(InventoryItem newItem)
    {
         if(owner.strength >= GetTotalMass() + newItem.mass)
         {
              items.Add(newItem);
              return true;
         } else {
             return false;
         }
    }
    public void DropItem(InventoryItem newItem)
    {
       items.Remove(newItem);
    }
    public float GetTotalMass()
    {
         float mass = 0;
         foreach(InventoryItem it in items)
         {
             mass += it.mass;
         }
         return mass;
    }
    public InventoryItem DrawItemsGrid(int columns)
    {
          Texture2D[] textures = GetTextures();
          currentlySelected = GUILayout.SelectionGrid(currentlySelected, textures, columns);
          return items[currentlySelected];
    }
    public Texture2D[] GetTextures()
    {
         List<Texture2D> textures = new List<Texture2D>();
         foreach(InventoryItem it in items)
         {
             textures.Add(it.icon);
         }
         return textures.ToArray();
    }
}

public class Player : MonoBehaviour
{
    public float strength;
    public Inventory invent;
    public Hat myHat;
    public Sword mySword;
    public Sword myOtherSword;
    void Start()
    {
         invent.Init(this);
         invent.Add(myHat);
         invent.Add(mySword);
         invent.Add(myOtherSword);
    }
    public void TipHat()
    {
        //play a hat-tipping animation!
    }
    public void Attack()
    {
        // swing a sword
    }
    void OnGUI()
    {
         InventoryItem currentItem = invent.DrawItemsGrid(2);
         currentItem.DrawGUIInfo();
         if(GUILayout.Button("Activate " + currentItem.itemName))
         {
               currentItem.Activate(this);
         }
         if(GUILayout.Button("Drop " + currentItem.itemName))
         {
               invent.DropItem(currentItem);
         }
    }
}

public abstract class InventoryItem
{
    public string itemName;
    public string dragInfo;
    public float mass;
    public Texture2D icon;

    public abstract void Activate(Player player);
    public void DrawGUIInfo(){ GUILayout.Label(dragInfo); }
}

[System.Serializable]
public class Hat : InventoryItem
{
    void Activate(Player player)
    {
        player.TipHat();
    }
}

[System.Serializable]
public class Sword : InventoryItem
{
    void Activate(Player player)
    {
        player.Attack();
    }
}

That's a start. I'm not offering any guarantees, since I'm pulling this out of thin air here. Give it a shot!