I have an entity that stores an itemstack in nbt and when it renders it uses that stack. However, when I unload and reload the world, the read/write to nbt is only called server side so according to the entity it's stack is null and it doesn't render. How would I fix this?

Welcome to client-server disparity.

 

You'll want this:

 

public Packet getDescriptionPacket() {
	NBTTagCompound nbtTag = new NBTTagCompound();
	this.writeToNBT(nbtTag);
	return new Packet132TileEntityData(this.xCoord, this.yCoord, this.zCoord, 1, nbtTag);
}

public void onDataPacket(INetworkManager net, Packet132TileEntityData packet) {
	readFromNBT(packet.data);
}

 

Assuming your read/write functions handle your TE's item contents.  If it doesn't, it should.

It's not a tile entity though =P

Just plain entity. Is there anything like it for them?

There's onItemPickup for EntityLivingBase...

It's not an entity living either =P

Just a plain entity. It's a projectile that renders as it's itemstack and when the player collides they pick up that itemstack.

Use EntityJoinWorldEvent and send a packet to client side.

Ok, can someone please tell me how to use packets? I've been told they're very easy to do and almost every problem I've encountered in my modding adventures seems to be fixable by packets, but I have no idea how to use them and the post on the wiki is unhelpful. If someone could slowly walk my through them I would be very much appreciative.

The wiki basically explain everything you need to know.

For practical examples, look at any open source mod. There is a high chance they use packets.