I've never forgotten my straps but, on a flight to LFAT with another pilot with me, we were half way across the water when we realised we had both forgotten to put our life jackets on.
As I approach 70 I am only too aware of real senior moments in my non flying activities but, so far, the only flying ones I will admit to are forgetting to start the descent in a normal circuit after a cross country flight. Just as well I enjoy sideslipping and glide approaches.