Same here. The dreaded "what if I need it? What if we miss it?". I do one of two things (but I still struggle), ask myself "would I buy this right now again?" or just put it away in a box out of the way. A few months later I find these boxes and I'm surprised at all the stuff I forgot about. I then have a much easier time donating them.
And when I think of all the things I gave away, I don't remember most, and I think I've regretted only one or two items out of hundred.
Still what works best: I watch a bit of hoarders. That makes me itch to de-clutter.