6. The one I always give as a gift.
There isn't 'a' particular book I'd give as a gift because I'd only give a book that I knew the recipient would appreciate. That said, I did buy Mr D and my Dad the same book about the restoration of the Vulcan XH558, because they both love military aircraft, so I knew they'd both enjoy it.
7. Forgot I owned it.
I was having a sort out in the loft with Mr D a few years ago, and I forgot that there was a crate up there with a load of books I put away because I didn't have room in my bookcases any longer, but I couldn't bear to just give them away. One of these books was a lovely old hardback version of Lord of the Rings, beautifully illustrated, and I actually couldn't think back to why on earth I put it up there in the first place. Needless to say, it came back downstairs to my office and has stayed there ever since.
8. Have more than one copy.
There are a number of books I have in paper copy and in Kindle edition too. One that I can think of is A Short History of Nearly Everything by Bill Bryson