Your boss…

Your boss is not your friend. Your boss is not someone you can trust. Your relationship with your boss needs to be entirely professional.
Do not do your boss favours. No working for free. No doing unreasonable duties. No working outside the hours you state as available.
Do not say anything to your boss. About anything. Keep it work related. They will only use personal information against you.
Know your rights. Know the laws. Your boss will come at you trying to get you to quit like its a favour to you. Its usually because they can’t legally fire you.
Be wary around your coworkers. Some will have no problem passing things along to your boss. Such as your mental health or financial standing
Never offer to pay for anything lost, stolen or broken. Especially if money is missing from the till.
Demand safe working conditions.
Your boss is only there to exploit your labour for profit. Unfortunately you need that labour to sustain yourself. Just be careful.