can you use a backpak with a hip seat?

[wads]

need to travel with 3 kids in the summer, & am thinking of getting a hip seat but can you use a largish backpack with one?

bump in case anyone knows...

Yep, I do it alot, as I take a big rucksack to put my shopping in at Tescos, and have also travelled by train with that set up. Its a bit tiring on your back if you're carrying all that for a long time though! But no probs for, say, a couple of hours, and no problems with balance or weight distribution.