Kodi and a MicroSD card full of local media files. Boom, Steam Deck becomes an offline entertainment kit that’s a one stop solution while traveling… Bored of games? Watch some movies or a show. Go back to games when your mood changes. Bring your dock and plug it into your hotel TV for either.
This is not an ideal scenario however. Your power bank will attempt to recharge the Steam Deck as fast as possible and lithium ion batteries lose efficiency as draw increases. The most efficient route would to instead run the deck, charged at 100%, off your battery bank until that bank is depleted, then allow the deck to run off internal batteries.
That said, as the Deck charges in the 20-25w range, this efficiency gain would be eliminated if your game demanded 20-25w system power.