package net.notanothercraft.mintcraft;

import cpw.mods.fml.common.Mod;
import cpw.mods.fml.common.event.FMLInitializationEvent;
import cpw.mods.fml.common.event.FMLPreInitializationEvent;
import cpw.mods.fml.common.registry.GameRegistry;
import net.minecraft.creativetab.CreativeTabs;
import net.notanothercraft.mintcraft.item.*;

@Mod(modid = "mintCraft", name = "MintCraft", version = "0.0.1")
public class MintCraftMod {

    @Mod.Instance
    public MintCraftMod instance;

    public CreativeTabs mintCreativeTab;
    public ItemCoin itemCoin;
    public ItemCoinBag itemCoinBag;

    @Mod.EventHandler
    public void onPreInit(FMLPreInitializationEvent e){
        mintCreativeTab = new MintCreativeTab();

        itemCoin = new ItemCoin();
        itemCoin.setCreativeTab(mintCreativeTab);
        GameRegistry.registerItem(itemCoin, "coin");

        itemCoinBag = new ItemCoinBag();
        itemCoin.setCreativeTab(mintCreativeTab);
        GameRegistry.registerItem(itemCoinBag, "coinbag");
    }

    @Mod.EventHandler
    public void onInit(FMLInitializationEvent e){

    }

}

package net.notanothercraft.mintcraft;

import cpw.mods.fml.common.Mod;
import cpw.mods.fml.common.event.FMLInitializationEvent;
import cpw.mods.fml.common.event.FMLPreInitializationEvent;
import cpw.mods.fml.common.registry.GameRegistry;
import net.minecraft.creativetab.CreativeTabs;
import net.notanothercraft.mintcraft.item.*;

@Mod(modid = "mintCraft", name = "MintCraft", version = "0.0.1")
public class MintCraftMod {

    @Mod.Instance
    public MintCraftMod instance;

    public CreativeTabs mintCreativeTab;
    public ItemCoin itemCoin;
    public ItemCoinBag itemCoinBag;

    @Mod.EventHandler
    public void onPreInit(FMLPreInitializationEvent e){
        mintCreativeTab = new MintCreativeTab();

        itemCoin = new ItemCoin();
        itemCoin.setCreativeTab(mintCreativeTab);
        GameRegistry.registerItem(itemCoin, "coin");

        itemCoinBag = new ItemCoinBag();
        itemCoinBag.setCreativeTab(mintCreativeTab);
        GameRegistry.registerItem(itemCoinBag, "coinbag");
    }

    @Mod.EventHandler
    public void onInit(FMLInitializationEvent e){

    }

}

Fix bag creativetab