I'd recommend arriving at the Eremitani Museum by 9:30. That's where you show your ticket. As I recall, they had a checkroom for coats and bags. The museum opens at 9:00 and is well worth spending some time in, before and/or after your chapel visit. They'll tell you when to start down the short path to the chapel so you arrive a few minutes before your scheduled time, minimizing time out in the cold. I don't remember whether others had camera bags in the chapel, there were plenty of cameras but mine is pocket-sized. You may have to ask at the museum. At the chapel, you'll spend 15 minutes in an orientation area watching a good film, then have your time in the chapel.