A practical consideration in selecting a day pack for a day tour is size. In Europe where snatchers are said to be common, security feature is a must. When the weather is unpredictable, versatility is an advantage. If you hop from one mode of transport to another, you want one that is durable. Should you lug your pack for over a week, you want comfort too.
This 30 liter pack held my soft shell breathable and waterproof jacket which was handy with the sudden downpour and the sudden drop in temperature, a semi pro camera, Lonely Planet Books, pocket French and Italian dictionaries and train maps, cell phones, extra shirts, portable power supplies, literature and shopped items. At times when the occasion called for formal outfit, dress shirts can be inserted. For hydration, a liter of water in an aluminum bottle was indispensable.
Zippers were tough and had handles with holes that can be inserted with a portable keyless lock.You can zip in and out several times an hour without a snug. Compression straps were added security to me. Material was made of ballistic which was light, durable and waterproof. Lastly, even with weights of miniature replicas of the popular landmarks in stone were packed, the shoulder bag held.
But at the end of the trip, this compact back pack had to be rolled. By airline standard, it was a count so it had to be packed inside a bigger soft back pack. Eventually, the Habagat day pack I have been using in most of my trips still prevailed.