Navigation electronics
Paper first, plotter second. Batteries die, charts don't.
Paper first, plotter second
Electronics are wonderful until the battery dies or the screen goes dark in salt spray. A paper chart, a pencil, and a working compass will get you home when nothing else will.
paper chart the backup that never fails plotter convenience, not truth compass the only instrument you can't turn off log speed through water, by feel too
Two backups, minimum
Position, depth, and heading each deserve a second source. Phone, tablet, and plotter all running off the same battery is one backup, not three.
Know your fix without the screen
Every few hours, work a fix the old way — a transit, a bearing, a sounding. When the electronics go, the skill is already warm. It's the cheapest insurance aboard.