I've done this in the past, and I would pull up the route in Maps on the tablet and then take it with me. But that doesn't handle getting lost, or last minute detours, etc.
Seems like keeping an iPad with cellular data around would be a good solution, but it starts to risk being "too good."
Nokia has dumb-ish phones which can act as wifi hotspots (e.g. the 8110 4G which runs KaiOS). So an alternative would be that + tablet, if you really need to you turn on the hotspot and can connect to the net.
Seems like keeping an iPad with cellular data around would be a good solution, but it starts to risk being "too good."