There is a point on Saturday morning, usually between nine and half past, when the queue stops being a good sign and starts being a problem. People at the back look at the line, look at their phone, and leave. The ones who stay are irritable by the time they reach you. One till cannot serve a queue that long, and a second lane, opened at the right moment, is the difference between a great Saturday and a merely busy one.
Here is how to run two lanes well, and how the loyalty card fits into it without slowing either one down.
Decide the trigger before the day
The mistake is opening the second lane when the queue is already out the door. By then the person who would run it is mid-task, the float is not counted, and the first six customers in the new lane watch someone set up a till. Decide the trigger the night before: when the queue passes the bread shelf, or the fourth table, or hits eight people, lane two opens. Whoever is on the floor knows that and moves without being told.
Count the second float before you open. Put the second device for stamping on charge overnight. Have a second QR card ready to prop next to lane two, because the one by lane one is no use to someone standing three metres away.
Split by task, not by half
Two identical lanes is the obvious split and often the wrong one. A cafe does better with one lane for takeaway coffee only and one for everything else; the coffee lane moves fast and the people in it know they are in the fast one. A bakery does better with one lane for bread and one for pastries and coffee. A butcher does better with one person serving and one person on the till and wrapping, which is really a second lane in disguise.
Whatever the split, say it with a sign. A queue that does not know which lane is which forms one long one anyway.
Stamping in two lanes
This is where the paper card falls over. Two stampers, two ink pads, and a customer in lane two whose card got stamped in lane one last week by someone who used a different stamp. Nobody can tell what is real.
With the card on a mobile number, both lanes work from the same Members page on two devices. A customer says their first name or last digits, the person on the till finds the row and presses Stamp. Each press is recorded one at a time against that member, so if both lanes somehow stamp the same person in the same second, the count still comes out right; nobody is doubled up or lost. The reward code, when a card fills, appears on whichever device pressed, and the card has already restarted.
One account, one login, as many devices as you have hands. Sign out of any device that leaves the shop.
Joining in two lanes
Saturday is the day most people join, because Saturday is when people are waiting with their phone out. The QR by each lane is how they do it: scan, type a mobile, enter the code, press Join. It takes about as long as the coffee takes to make. The person on the till does not have to do anything except say "scan that if you want a card".
Do not try to join people for them. There is no way to, and on a busy Saturday you would not want one. The customer does it while they wait; the staff member stamps when they reach the till.
If the shop is on the Free plan and hits fifty members on a Saturday, the join page tells the fifty-first person the club is full for now. Move to Regulars before the next Saturday and it opens again.
Rewards at the till on a busy day
When a card fills, the code is on the row and in the note next to the button. Hand the reward over then, while they are at the till, even in a rush; it takes two seconds and it is the moment the whole scheme exists for. If the customer would rather save it, the code stays in the Rewards waiting column and they claim it next time. Do not make them remember a code; you have it.
Close the lane cleanly
The second lane should close when the queue drops under the trigger, not at a fixed time. Count the float, sign the device out or hand it to whoever is staying on, and move the QR card back to where it lives. The staff member goes back to the floor or the bench.
The Saturday after
Open the Members page on Monday and look at the joined dates. A good Saturday with two lanes will show a cluster of new members from that morning. That is the measure: not how long the queue was, but how many of the people in it will be easier to serve next time because they are already in the club.