There are quite a few apps with which you can download the maps for use when not in service.
Carry a big external battery pack.
I have two with 8 cells each.
ABC [Always be charging]
I do have some topo maps downloaded for some States [Mont., Colo.], but could use more.
If there is a local Orienteering Club in your vicinity, spending a number of afternoons running around on their courses is good training for going off on your own.
I think my downloaded maps are for my older Garmin unit [which I do carry when going off well known paths].
I carry extra batteries for it too.
A day pack can get heavy in this electronic age.