Some colleges also give you padlocked storage areas within your room... for example most rooms here have fitted wardrobes with a lockable compartment above where I can fit my printer, mini-fridge, laptop speakers, kitchen stuff, posters, half-full bottles of toiletries... basically everything I actually want to leave. Even if there is some storage available of course you still have to move out of your room so someone else can use it over the holiday, and the nicer your room and the more modern your accomodation the more likely it is you'll have to do this.
Generally you're likely to find better access for moving in and out with the further out colleges, but because these tend to be the newer ones they're also the ones which host conferences, so you're more likely to have to move out in the holidays!
The heaviest things I have to carry backwards and forwards tend to be boxes of work (which increase with each year sadly) which I wouldn't want to leave here in the holidays anyway as I have vacation work to do.