From my experience, you can win up to 0.01 BTC with 0.001 deposited on a new gambling site during a promotion. Only you shouldn't be too greedy thinking "What if I deposit 0.1? I can win 1 Bitcoin then!". Remember, dealing with newly appeared gambling sites is still very risky, and you might never see your deposited money again. And not because you can lose them to a game, but because you wouldn't be able to withdraw your balance from that site.
I know it was risky, but 0.001 is what I can afford to lose. With this approach I lost around 0.002 to a couple of scam sites, but I won and withdrew more than 0.02, I mean, ten times more than what I lost, participating in promos of newly appeared gambling sites. I'm not encouraging anyone to follow my example, because if I were depositing to every new site, I would in negative profit from this activity currently. Most new sites have so many red flags that I don't even consider playing there, let alone depositing my money. But those are "red flags" to me, because I have some experience in the field, and they can go unnoticed by inexperienced gamblers.