We're downsizing, too and so far I'm being fairly ruthless, but my husband is still insisting on taking all sorts of stuff with us 'in case we need it' - I'm talking about planks of wood, old melamine slabs, rusty tools - you name it, he wants to take it. It's not as if he's physically able to make a cupboard anymore!
Anyway, I have thrown lots of mementos away - son's first tooth, daughter's first lock of hair, their early medical records, old birthday cards - a heart-breaking task. But as I reasoned, most of it had just been transferred from attic to attic over the years, had never been looked at, and the boxes even smelled of damp. So out they've gone.
I've just had one regret so far and that was throwing out my son's last day at school shirt with all his classmates' good wishes and funny comments written on. I stupidly put it in the wash to get rid of the damp smell, but when it came out, the comments had been washed off, so I ended up throwing it out. I wanted to show it to him when he visits from Australia in the New Year. My daughter saw hers, and she said it brought back some great memories.
It is a difficult task.