What size crossbody bag is best for travel?

Across the reviewers we read, 5L–7L is the sweet spot for sightseeing days: enough room for a phone, wallet, sunglasses, a compact water bottle and a light layer, without crossing into backpack territory. Sub-3L slings (like the Bellroy Venture Ready 2.5L) work best as pocket-replacement EDC, while 9L+ bags get heavy on a single shoulder.