Or, if all you need to carry is a lunch or a spare sweater, you could use a bike handlebar bag. A rack secured to a vintage racing bike’s seat stays with P-clamps. Eve O'Neill/NYT Wirecutter ...

The bag is waterproof and works best on any flat, alt, or drop bar bike with a front rack, but the DX35 also features a removable GEARLID that makes the contents accessible while on the go There ...