Frankly, your spending is so low that you will never really accumulate anything of value - one free regional economy flight every 5 years maybe? Your miles will expire before you can use them in most cases. You're obviously flying on the lowest possible economy fares, which earn few or no miles.
For the small stuff I'd take it back as credit card rebates of around 2-3%. See here for the best deals:
https://www.hongkongcard.com/forum/show/4979
But 2-3% on 3000 per month is close to negligible; as a relatively poor retired guy I put about 25000 per month on my cards. If you're trying to live in HK on the sort of money that requires you to shop and eat in places that don't take credit cards then I suggest that earning airline miles is the least of your problems!