Remove stored card numbers from the shops where you spend on impulse. Unsubscribe from their marketing mail and reply STOP to sales texts you did not ask to keep. Delete the shopping apps you open when you are bored. None of this blocks a real purchase. It adds a minute, and a minute is often enough.
A small note on the card you use most can help too. A phrase such as “Is this in the plan?” is a private reminder, not a lock.
Start this week
Remove your card from one store account and unsubscribe from that store’s emails.