Where should a cyclist secure his valuables before entering a store that forbids carrying bags into the building?
Normally, when cycling, I carry my wallet and phone in the small compartment of a backpack, and I carry my shopping home in the large compartment. I have occasionally carried large or heavy things home by securing a bag to my bike's rack using bungee cords. I've considered buying grocery panniers to hang on my bike's rack, but I prefer to carry my backpack with me while inside a building because I fear that opportunist burglars will open an unlocked bag left on a bicycle and steal its contents.
But today (2017-09-11), on the front door of the Salvation Army Family Store at the corner of Fairfield Ave and Jefferson Blvd in Fort Wayne, Indiana, was a sign forbidding carrying bags into the store. The manager, when asked, refused to either give an exception for cyclists or recommend a secure place for cyclists to store their bags while shopping, on grounds that the manager had to reimburse another customer for a backpack and contents thereof that had been left in the store's former bag check and subsequently stolen. When pressed for an alternative, the manager said something to the effect "I can't tell you how to live your life" and actually recommended that I leave my bag outside unattended. I imagine that this would prove even more attractive to thieves. So I did not enter the store, and I did not spend money in the store.
Is there a practical way for a cyclist to shop safely in a store like this? Answers to "Ever seen a locking bag that could be locked to the bike?" look expensive; I had wanted to avoid spending a fortune that defeats the purpose of shopping at a thrift store in the first place. Or should a cyclist just review this store in as many places as possible (Yelp, etc.) as being impractical for cyclists?