You are asked to go up to a window, a few things are checked and you hand over your documents then sit back down to wait to be called for your actual interview. I only had a few documents though so it wouldn't have warranted a divider, I just had them in a clear plastic folder. They are very unlikely to take any new docs, they just want what is on the checklist. And yes, a backpack is fine as long as it's not too big.
Good luck.