Aww that’s pretty lax but this is London ‘blink and it’s gone’. May I suggest a phone reminder call? Either that or attach your arm somehow loosely to the bags and this can never happen again.
I know the feeling so well when you’re tired and things slip the mind. String (or elastic) attached to your person rarely fails to to go wrong even when your mind is tired or elsewhere.
Soz and good luck for future boris bike use x