I would invest in something like trading or gambling just for the fun its not that its necessarily to invest it into something good right ?
It was not asked if it should be something right, but it was obvious that the guy needs an idea on where to invest it and that means the OP needs some idea on how to earn more from his regular $40 earning each day. With that, I am sure that OP needs something that earns, so your first suggestion is good but the second which is gambling, that's off!
I don't know there are people that are suggesting some investments just for fun. It would be fine if the money that will be invested is just going to be for fun too. Gambling for fun will surely ripped off your pants easily and that $40 will not even be enough if you drag yourself into addiction with it, trading would be better.
I think, everyone is telling about the gambling, because they also know that $40 is not enough amount. But personally, i also don't suggest him, fun wise gambling is good, but investment wise, should chance the way. Also i agree with you, trading is better, because in trading, you can earn instead of gambling.