Lol. Yes, a car boot is the car trunk. And no, the trunk isn't always locked. If you leave a car open then the trunk is open too along with the doors. So the lesson is LOCK THE F***ING CAR when you go and that way your stuff is out of sight in the TRUNK, not tempting an attempted break-in because it's been left in the car within sight, and the car doors (and trunk) can't be opened either. Your camera will then most likely still be in the TRUNK when you return lol.
It ain;t difficult really. I've lived out of a car for 3-4 days at a time, leaving everything I own in it and going to all sorts of remote places and never been robbed or had my car broken into. A few simple common sense (if possible !) steps and it'll be someone else's car that gets done over.
Number of people I hear say that their car was open when they got back ... FFS, no-one has a master over-ride key for modern cars. If it's open when you get back YOU LEFT IT OPEN, easily done after a few days on the razzle, and you only (unfortunately) have yourself to blame for the consequences !!!!