This is the third kid I've worn in my Trekker baby carrier and I just figured out how to make it more comfortable when carry my diaper bag at the same time:
Put the diaper bag on my shoulder before clipping the second strap or put a carrier strap through the diaper bag handle.
No child was awakened during the taking of these pictures.
My shoulders started aching with the memory of lugging my kid in the Baby Bjorn AND the diaper backpack. Those were the days! (Now he's taller than I am.)
More: Hacks for baby carriers