I think we need a big bankroll to run up slots. You shouldn't buy bonuses directly; instead, hunt for them by placing smaller bets and setting the game on auto for around 250 spins. You're likely to hit a bonus at a comparatively lower cost
The Martingale betting system involves doubling your bet after every loss, with the aim of recovering previous losses and making a profit. While this strategy can be effective in the short term, it carries the risk of significant losses during a losing streak.