This particular bag has a 17-litre volume. Maybe not a good choice if you prefer lots of colour choices, but it does come in grey.
From Amazon
RIVACASE Backpack with Laptop Compartment (15.6 Inches) and Tablet Pocket (10.1 Inches) - Trolley Strap for Rolling Suitcase Water Resistant Material / 7760, gray, 15,6 pouces, Modern
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Laptop Case Rivacase Suzuka Grey
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