In the Supermarket

Okay: This is the second post of the day, just seconds after the first. But something happened that I missed by just three minutes and I am so angry with myself for not seeing it and taking care of it that I want to write it out so that I will not forget next time.
I was in a grocery store and in front of me on line was a nice young woman--I later found out she's a local teacher, though not at my daughter Madeleina's school--who had bought a bunch of what was obviously going to be dinner. She had lettuce, onions, garlic, a big tomato, some chopped meat, a small sour cream and a can of refried beans, a can of red salsa and some tortillas. So she was a mom going home to make a fast and inexpensive dinner for her husband/kids.
Well, she paid with a check but didn't have her driver's licence so the store wouldn't accept it. She did have her Burleson, TX teacher's badge, with her picture, but the store wouldn't accept it.
She was very embarrassed when a manager was called over and she was told they knew her but corporate wouldn't let them accept a check without a driver's license.
I waited patiently in line, and when she apologized I told her not to sweat it, this sort of thing happens to everyone.
And a few minutes later, when the lady's order was cancelled and I was finished and in my car it suddenly hit me that I should have just paid for the lady's groceries. It was a lousy $14 bucks or so. I just didn't think of it till I was already in my car.
So now I feel like a schmuck for not paying more attention. That poor lady went home without dinner and then probably had to go back out to rebuy that food to feed her kids, and I could have handled it for her if I'd just been thinking more clearly and less selfishly. Dammit. I hate catching myself messing up.
Next time I come on that sort of thing, I will try to remember to simply handle it.