Walmart (the parent company of Sam's Club) has been testing a service called Shop & Go for several years now. The idea is that you shop normally, scan in items with a barcode app, pay from the app via a credit card/debit card/store payment system, then just walk out the door - no need to go through a checkout line at all. Previously the program was limited to only a few hundred stores and it only worked on the iPhone, but it looks like the company is ready to put a more widespread version out for the Sam's Club bulk retailer stores.
Sam's Club Shop & Go works just as described above: scan in your items as you shop, pay, then leave with your stuff. You'll need to show your receipt to the attendant by the door as you leave, but as I recall, that's standard policy at Sam's Club anyway. It could save a ton of time, even versus the newer "self check-out" machines.
There seems to be just one hang-up: the app has some kind of location feature where you have to be physically located at a store before it allows you to begin shopping. Early Android users are reporting that the system sometimes can't locate the user's position, and thus won't allow them to shop. If Sam's Club can work that out, it should make the experience much smoother. A similar app may or may not come for Walmart stores in the future - the larger, rarer Sam's Club stores would seem like a good testing ground for a bigger program.
The program has gone nationwide in October 2016. Sam's Club provided us with the following statement:
We first began testing the current version of Scan & Go in October 2015 at our club in Fayetteville, Arkansas. The initial one club pilot lasted for four months before we expanded the service to 24 more clubs in February 2016. We continued to roll out more and more clubs this past summer and then completed our national rollout to all 645 clubs in the U.S. in October 2016.