回複：Just show them what's in your bag and explain

If it's a grocery supermarket near your house then probably you have the membership card. Whenever checkout you will scan the card/tag to get discount. Then your shopping history will be recorded in the database. Unless you didn't feel confident, you can let the store to look up the shopping history and point out those 'tiny' thing in your bag from the list. That will be the evidence you can use even it's may be not so accurate.