For produce, you could turn the shelf into a scale. It reads X before the camera detects the customer picking up the item to put in their cart, and it reads Y after. Therefore the potatoes they picked up weigh X-Y.

Another approach would be to have a scale and require them to stick their potatoes on it, but not require the other, tedious steps like entering a PLU code or printing a sticker. If you can track them picking up items off a shelf and putting them in their cart, presumably you can also track an additional intermediate step where they put it on a scale. (And connect that scale to the network, take a reading when you see them stick potatoes on it, and correlate that.)

Of course you can always just sell by unit and not in bulk. Sell 1 pound, 2 pound, and 5 pound, and 10 pound bags of potatoes instead. Maybe even 0.5 pound if someone wants a small quantity. Or for things whose size doesn't vary much (like apples), just sell by number of apples.

For steak, the packages are normally already weighed and labeled, so the problem might be easier if you can just scan a label that's already printed.