Birthday/Christmas cards - I kept every single on from my Mum, Sister, DH and Dad and the boxes were bulging. I decided this year that it's ridiculous keeping them since I never look at them again. I had this notion that after they'd 'gone' I'd read them and know I was loved but I know that without reading a shop bought card right?
Handmade ones I keep because I appreciate the effort involved. I threw 5 years worth of cards out this year and will endeavour to do the rest as soon as I can get to them.
Travel and memorabilia - I have a big box labelled mementoes. I stash all my tickets, maps and connected things in here with a view to making mini scrapbooks at some stage - so maybe keep them for now Pixie.
Books - keep them if you love them, but treat them with kindness and find a neat and tidy home for them. Stuffed under the bed is not it
Hope that helped a bit, you're doing great. Hoarding is a hard habit to break. I salute you for your efforts Pixie!