I printed off a copy of all reservations (airline, hotel, list of ADR location/time/confirmation numbers).
Made an excel spreadsheet with a little chart for each day that could be printed to wallet size (I was traveling with extended family and wanted each group to have a copy, so I wasn't the only resource and on-site tour guide!) It listed our chosen park, FPs for the day, ADRs, notes about parade or fireworks or show times we may want to keep in mind. Park hours for our chosen park bolded, all other park hours listed too, in case we changed our minds.
Printed off the Cheat Sheets from Easy WDW and put notes on the back of any particular QS restaurants I thought we might want to aim for, little-known attractions/shows/hidden gems I had found out about during planning. You'd think it would be committed to memory after all the researching, but there's just SO MUCH there, it's easy to forget details.
Once at the resort, I put the resort activities schedule in the binder that listed poolside parties, evening movies, etc.
Photocopies of any gift cards and our credit cards in case of lost/stolen wallets that needed to be reported.
Memory Maker and Disney IT phone numbers - i had used these during planning and figured in case I ran into tech troubles on site, I'd want them handy. Luckily ddin't need them!