I thoroughly the read the guidebooks for the countries we will be visiting. For several years, I have carefully ripped out the few pages for each location that I want with me. If you bend it backwards sharply at that page, they will carefully come out intact. So, for instance, I want the city walking tour info & the highlights that are of interest, don’t need the hotel or restaurant pages, and might want info that says specifics for a train or bus situation- where to buy tickets/ this train station doesn’t sell tickets, etc. Usually this is not more than 3-4 separate pages. I staple those together as you mentioned, along with a page of extra info from my research. When we are traveling on the train, I pull out our next tiny packet, and we review our options. (If I’m traveling solo, I will read the few pages again while I’m waiting for my lunch order to arrive.)
I don’t throw these away. When we’re back home, I place the pages back into the book and secure with a large rubber band. I like to refer to them when we’re returning to the same location again. Since I’m only bringing a very small subset of the book, it’s not heavy to bring home.
I don’t use the guidebook recommendations for lunch, but I do find some restaurants during research that I would like to try, so I add them to the TripIt app. Also any activities I want to be sure to do. Since using TripIt for a few international trips, the physical pages of info I bring has diminished.