Item pickup.

// This goes in the tick.
List<EntityItem> list = this.worldObj.getEntitiesWithinAABB(EntityItem.class, this.boundingBox.expand(0.5D, 0.5D, 0.5D));
for (EntityItem entityItem : list)
    if (entityItem != null && !entityItem.isDead && !this.worldObj.isRemote && entityItem.delayBeforeCanPickup == 0)
        this.pickupItem(entityItem);


// New method.
protected void pickupItem(EntityItem entityItem) {
    this.worldObj.playSoundAtEntity(entityItem, "random.pop", 0.2F, ((this.rand.nextFloat() - this.rand.nextFloat()) * 0.7F + 1.0F) * 2.0F);
    boolean flag = true;
    // This is prolly unneeded for an inventory.
    for (ItemStack item : this.itemList) {
        if (item.itemID == entityItem.item.itemID && item.getItemDamage() == entityItem.item.getItemDamage()) {
            if (item.stackSize + entityItem.item.stackSize <= item.getMaxStackSize()) {
                item.stackSize += entityItem.item.stackSize;
                flag = false;
                break;
            } else if (item.stackSize == item.getMaxStackSize()) {
                continue;
            } else {
                item.stackSize = item.getMaxStackSize();
                this.itemList.add(new ItemStack(entityItem.item.itemID, item.stackSize + entityItem.item.stackSize - item.getMaxStackSize(), entityItem.item.getItemDamage()));
                flag = false;
                break;
            }
        }
    }
    if (flag)
        this.itemList.add(new ItemStack(entityItem.item.itemID, entityItem.item.stackSize, entityItem.item.getItemDamage()));
    entityItem.setDead();
}