Various Android apps that are useful when you're operating off the grid, particularly when you only have GPS + compass, but no cell connection.

specifically for offline navigation

• Backcountry Navigator
• Maverick
• Backpacker GPS Trails
• GPS Grid Reference

store map layer data offline

• the stock Google Maps app has the ability to do this, via Settings > Labs > Pre-cache map area

waypoints / tracks

• Turbo GPS 2
• GPS Venture
• Open GPS Tracker
• GPS Essentials

GPS/compass without any map layer

• Compass

other utilties

• GPS Essentials