Been using eBags for # of years now, the Mother Lode TLS Weekender 22" MLC has almost 3,300 ci capacity unexpanded, there is a smaller junior one - in terms of value for money & lifetime warranty, it's unbeatable.

Used a custom shoulder strap as I've only use the backpack straps twice on very heavy loads thru airports in transit. There are compartments for just about everything.

A compact shoulder/messenger bag (i.e. Timbuk2 or STM) that fold flat will easily fit on the huge outside compartment or in the back's hidden computer "bay" for a day trip.