iOS/Android: The Maplets app allows you offline access to public transportation, city, park, and other maps on your mobile device. The app costs $2.99, but you can use it to find downloadable maps for almost any trip location.
On the iOS version you can also make notes on the maps by dropping a pin or drawing a a route. There are also Maplets apps specifically for bike routes, metro, California state parks, and Canada. Give Maplets a try for yourself by downloading the app, linked below.