Audax rides

KRYPTONITE KRYPTOFLEX R2 RETRACTOR POCKET COMBO CABLE LOCK

Or something more substantial in your support vehicle

https://hiplok.com/product/zlok1/

(For quick stops)

I've never brought one and it's always been fine. There's always likely to be people around the controls and I normally stop at bigger supermarkets and will bring the bike inside.

I carry a cheapie key lock cable from Halfords that wraps around the seatpost or one of those Abus combination cable locks.

I ride a lot more DIY/Perms so I'm solo much more often than your usual audaxer.

Either don't bother or use a minimalist cafe lock.

The only time your bike's really going to be on its own is either 2 minutes outside some newsagent in a village somewhere or on something like the Bryan Chapman, sat outside a remote youth hostel in the wet for a few hours. Not a bike theft hotspot

Travellodges, bring the bike in your room

As people say, get a cheap £5 combination lock or Hiplock, I've never needed anything more.