Amazons dead-set on killing off the grocery store, with a same-day delivery service and even a Dash gadget for restocking items around the house. Now the retailers going one step further, taking on Costco and Walmart with a new program called Prime Pantry. If youre a Prime member living in the 48 contiguous states, you can ship 45 pounds worth of household essentials — in everyday sizes, not in bulk — for a flat fee of $6.