After I put up a search engine for Amazon Prime items, I've started to notice what people really buy with Amazon Prime.
A large chunk is consumer packaged goods like toothbrushes, diapers, batteries, toilet paper, etc. The kind of items people buy at Costco and Wal-Mart in packs of 3 or 4: shampoo, vitamins, laundry detergent.
It makes sense. You save a lot of time, and the Amazon prices are usually as low or lower than the big-box warehouse stores.
So if you are the kind of person that buys a fair bit of stuff from Costco, Amazon Prime may make a lot of sense.