Backcountry Navigator for Android. Cost is $10 - the best $10 you'll ever spend on software. You can download a 25 square mile area you want to explore to your phone. That way you don't need cell phone or internet coverage to use the application.
I've used it extensively at my place in Ontario. Whether I'm on land going or by boat, the detail is amazing. For example, most topo maps will show elevation, this one will show me the portage location to get into that remote lake and guide me right to it. Old logging trails are also listed. In short, buy this app, - you won't be disappointed.