Just got back from WDW and my hubbie carried a large backpack everyday into the parks, and we never had an issue with taking the backpack with us on any of the rides. He usually just put it on the floor of the ride we were in, or for Soarin, he left it on the floor in front of him (because it wouldn't fit into the bag holder underneath his seat) and the CM just moved the backpack to the side of the row we were in, and we picked it up on our way out. I did see one person who had a rolling backpack (more like a small suitcase in my opinion!) that he wasn't allowed to take onto a ride (sorry, can't remember which ride), and he ended up turning around and leaving the ride area thru an exit. Bear in mind that we didn't go on Mission Space, or Space Mountain. We did go on the new Mt. Everest ride with the backpack with no problem. (Word of caution for those who experience motion sickness - I'd avoid Mt. Everest, I was sick most of morning after riding this ride, but may be due to just eating breakfast before riding; also, husband who doesn't get motion sickness also experienced some nausia (?sp) after riding.)