Puzzled why a bike cannot carry a rack and small panniers with change of clothing ?. You described a "credit card tour". You need a change of cycle clothing, some street clothes, rain gear, maybe warm sweater and tights, lunch snacks, toiletry items. If not a rack, a bike packing setup with a large front bag strapped on the h-bar and a rear under seat bag would probably carry all your stuff. Just Google "bike packing bags".