Amazon's dead-set killing off the grocery store, with a same-day delivery service and even a Dash gadget for restocking items around the house. Now the retailer's going one step further, taking on Costco and Walmart with a new program called Prime Pantry. If you're a Prime member, you can ship 45 pounds' worth of household essentials -- in "everyday sizes," not in bulk -- for a flat fee of $6. (Yes, that's on top of your Prime membership payment.) Rumors about an Amazon Pantry service began circling late last year, and while the service now appears to be live, the company hasn't formally announced it.