To answer your question, probably the lightest hubs use aluminum axles and cartridge bearings, like
https://mackhubs.com/hubs/track/low-flange-rear/ .
I would think that rather significant performance penalties would be worth it to avoid carrying an entire rear wheel. Maybe tubeless with a rather robust tire? Or even
https://tannusamerica.com/pages/tannus-armour with a robust tubed tire. Or even a fully solid tire.
Tannus Armor for tubes or tubeless with most tire inserts also will run flat more or less rideably if the distance is short and the handling is relatively mellow.