I agree, both trading and gambling are very risky in nature that you risk of losing all your hard-earned bitcoins. Since your question is only on growing it without considering how long it would actually take, then I think just passively storing it and trading it when it holds a better and greater value compared to the value you got it for. But, if you want a faster and more active way, then trading would be the best option, but you should first study or maybe gain some experience before starting of in that venture because it carries more risk as it gives better results. Gambling for me is a definite no no!