LOL, when you reach my age, you can look back on all the times you left your wallet/money/keys/camera at home, and went "oops" for real.
Heck, when I had my store, I had a customer leave her purse in my store. She had mentioned she was on her way to California on I-80, so I called the police next state over and they pulled her over. Of course, her DL was in her purse in my store. The entitled jerk told me to mail it to her in California. I mailed the entire purse, contents intact, and never heard back. She never sent a thank you or postage! If I'd known that when I mailed it, I would have taken the money out of the purse to pay the postage!!!
Just say, oh, hey, I left my id in my car. Leave and don't go back in.
Clerks see this CONSTANTLY, and won't think twice of it. Sometimes the customer comes right back in, with his id, but more often than not, he just gets in his car and leaves.