As mentioned, those 20x points on certain gift cards are a great source. I was desperate to reach minimum spend on a card so I put a $5,000 airbnb payment directly on a CC (stupidly forgot to go via Qantas site) but if I didn't need that I would have bought 5k worth of gift cards during the going promo and collected 50,000 QFF points. Same with Apple store. Bought an $800 ipad and pocketed 8,000 points.
I really need to get my in-laws onto a rewards card. They're farmers and they put a ton of expenses onto no-rewards (because they're no fees) CCs. They just don't want the hassle I guess and I don't blame them
