Have you ever heard of manufactured spend? It's a means of charging a credit card to accumulate points to meet the minimum required purchases - for example in the first 90 days of issue. Visa/Mcard may offer a new cardholder 20,000 miles if they spend $3k in the first 3 months. You go out and "purchase" groceries every week as above in the first post - getting a couple hundred bucks in your pocket each trip. You deposit the money in your bank and when the charge card bill shows -you've got 99% of the funds required to cover the bill. In 3 months - you really haven't spent but a few bucks - but get mileage credit as if you spent $3k. There are several other means of spending more and getting higher points - check out the reddit forum for more info/ideas:
https://www.reddit.com/r/manufacturedspend/