I've had a nice bike stolen before (Kryponite Ulock) - theft concerns was one of the main reasons I quit bike touring decades ago. Ultra- light/compact/portable got me to restarted again, and I can now take everything with me (eg., inside tent, stores, museums, restaurants, etc).

In your case, I'd just lock-up to a nearby tree. Another idea for few oz. is to covertly rig an alarm on bike while parked - go with mechanical switch (eg. door travel alarm or grenade-pin personal alarm) which doesn't eat batteries or suffer from false alarms.

I don't mind losing the bike so much - homeowners insurance covers it, but there's an awful lot of work and time involved in obtaining, modifying, and tailoring all those small accessories, gadgets, and doohickey's involved in camping and self-supported touring.