I usually keep them all together for the trip in one of the disney bags you get. I get a park map each day from each park I visit. I keep all the bags in one of those big plastic storage bins. Every once in a while, I open it up and go thru it. It is fun going thru the old memories.
For a bunch of trips, I also got Passporter books, Those I keep receipts in, and keep on the bookshelves. I've used the receipts- going thru them to see what I purchased on previous trips, to decide if getting a dining plan is worth it or not.
Bernie