Sports is also a good option, though quite a bit harder. Martingale with a low multiplier is never worth it as you'll very likely wager more to hit a certain profit target (ex 100%) compared to a straight all-in bet (2x multiplier if you're shooting for 100% profit). The more you wager, the more likely you are to lose as your theoretical losses increase. Otherwise, you're better off with a 9900x martingale strategy to get the highest change to double your money (~49.65% chance with a 1% house edge compared to 49.5% with a straight bet)
Yeah - sports is also possible but I also think its even harder than poker thats why I didnt mention it. Nice explanation as to why martingale is just old but definitely not gold...