@saikyo. I guess what you are looking for is a "sling bag". I love this format.
The sling bag is basically a single strap backpack to be used cross shoulder.
I like the style for every day carry... Specially because, it is easy to swing to the front while in a crowded subway, as a safety measure.
What you can do is use a Packing Cube Shoulder Bag like the Side Effect shown around 5 on this video. The shoulder bag has a volume of 4.5 L, that is three times greater then the Side Effect.
With more centered webbing lops like Side Effect have, the Packing Cube Shoulder Bag could become as versatile as itīs smaller cousin.
For the record:
I would love to have a smaller version of Tom Bihn Buzz sling bag, updated by Tom Bihnīs pragmatic design! :P
I am always asking for smaller formats because I downsized from notebook to a 8" tablet as my EDC.