I like this guy on Drawstring Bag

Essentials for the gym and short trips. This simple and stylish little specimen is ideally suited to easily store away the essentials. Put it on your back and you won’t even notice it’s there when out on short excursions or bike trips and roaming the urban jungle.

• Handy drawstring mechanism for easy opening and closing
• 12 litres holding capacity
• Quality: 130 g/m²
• 100% cotton