I put maps or cue sheets in the map cover on my Ortlieb handlebar bag. If you don't have such a thing, you can easily make a map cover out of office supplies. Report covers, duct tape, and strips of velcro to secure it all to your handlebars will do the trick very well.

Something I learned on my second-ever tour: Don't use an inkjet printer to print your cue sheet. The ink runs like crazy at the first decent rainstorm, even with a map cover.