While playing around with my bags tonight, testing out different configurations, I realized that if you unbuckle the Side Effect, you can buckle them right into the waist strap of any backpack. Very useful!
This is my husband modeling my Nordic Dyneema Smart Alec, and my Navy/Iberian Side Effect. I'm obligated to note that Greg only agreed to this on the condition that I describe him in the forums as "long-suffering". Uh huh.
You'd probably want to use some of those little velcro wrappeez thingies to reign in the cascading straps, but otherwise this works great, I'm going to use it on my next trip with my Dyneema Synapse 19.