[TannerS]

Having a barcode scanner to see how much items costs so you dont go over your limit, the device could even tally up all of the items you want scanned in a givin store so it gives you a total amount and if you want items off the list you can do so without having to rescan all items.

[a_guy]

This could be coupled with an app where you enter the list of your groceries, each time you scan an item it puts it off the list, that way you no longer have to worry about forgetting an item.

[Jay-Kopf]

For this you can take a camera module and need a barcodescanner app for the watch.