Rec for bike backpack with side zipper into main compartment I got a used SAG Life Air Force 1 backpack from a friend, after deciding that a messenger bag was just too heavy when it was full for my one shoulder to bear. I primarily use the bag for urban commuting, hauling everything from my work stuff and u-lock to groceries.

After using the SAG backpack for a year, I'm again on the search for a new bag. This one is good overall, and the capacity when it's extended and full is insane (this picture does it justice), but generally it doesn't fit me well. It's way too long in the torso, even when it isn't full, which I can tell by where the hip belt hits my hips-- more around my bum than waist. I suspect its too-big fit is because the bag is primarily designed for dudes, and I am a lady with a smaller frame. 

However, the SAG bag does have another, crucial, game-changing feature: a side zipper that allows me to get into the main compartment of the bag. This way, I can just slide it one-shouldered around to my front and get into the bag from the side, messenger-bag style,  without taking it off and unrolling the top. (This photo sort of shows what I mean with a laptop, but I can get into the whole main compartment of the bag this way.)

Are there other brands of stock (i.e. non-custom-made) bike bags that have this feature that make expandable backpacks? Is it something that anyone has seen on a bag that isn't a SAG Life bag? The other problem is that because this brand is Japanese, it's kind of hard to find in the U.S., so even another SAG bag with smaller dimensions might be hard to find so I can try it on before purchasing.

I've looked at Timbuk2, and as far as I can tell from the photos and product descriptions, the bags that they say have a "swing-around" feature, there's only access to the laptop sleeve, except with the Phoenix, which seems to have the same dimensions as the Airforce 1 bag and it doesn't come in other sizes. 

I've also looked at Chrome and Mission Workshop and neither company seems to have a bag with this feature. 

Am I going to have to go custom to get this feature on a bag that will fit me?
Most of the nicer courier bag/backpack companies don't do a zipper down the length of the bag because that creates a weak point for not only loss of contents, but water entry. Some will do laptop pouches, but if you're looking for a heavy duty courier bag it's slim pickings for external zippers into main compartments.

The closest I came to finding something like what you're after is from either Crumpler that have some laptop sleeves and/or zippers to main compartments or Freight Baggage that have a smaller secondary compartment that is easily accessible. I looked at RELoad, Freight, Seagull, Bailey Works, Trash Bags, Banjo Brothers and some other smaller companies.