National geographic trail maps. Search for it in the App Store its $2.99 and works better then any GPS I've used. You have to download the maps you need to your phone but you can get topo and arial and it works great when you have no service.
Buy the Back Country Navigator Pro application it is awesome. You can download the maps of the area you will be going into and they will work when your phone doesn't have service. I put my phone in airplane mode and it will last a long time. The topo maps are excellent. You can also buy the public and private boundary maps overlay which is handy when hunting areas with a lot of private land. If you have any more questions pm me and I will help as much as I can. Good luck