... which is pretty wide. There is a mesh pocket on the back of the hood at MK, but it is not large enough to hold a large bag. (It's big enough to hold a couple of water bottles.)
Here are photos from Deb Will's site:
http://www.wdwig.com/strol_faq.htm
You would want a bag designed to hang over a bar, or adapted to do it. Lots of folks use a bag with one long strap, and drape it over, but if you prefer a backpack, you may have to get crafty.
I have a backpack with d-rings on the shoulder straps, that are designed for hooking on keys, phone cases, etc. If you have a backpack with rings on the straps, or even a top loop, you could stick a couple of s-hooks on the stroller bar to hang it on. I don't know the diameter of the bar, but I'd say to make sure that the hooks will slip onto a 1.5 inch bar, just to be safe. (S-hooks are available in the chain section at the hardware store, or for use on wall-grid storage.) To illustrate, here is a set specially made for use on strollers, but the ones from the hardware store work just fine:
http://www.princelionheart.com/travel2.html#Stroller Cup
Those of us who have umbrella strollers have it easier for handle-hanging; it's one of the reasons why the umbrella-handle design is so great, IMO.