When you go on holiday, it isn't unusual to see people taking photo after photo, barely taking the time to focus. In fact, they're so intent on getting the shot that they don't even really look at the things they're taking photos of. When they look at them afterwards they probably have trouble remembering that they were there.
Writers are always told to carry a notebook with them, and I second that, but there's a danger of becoming like those photographers. Somehow a balance needs to be found between observing and recording. Be too quick to write things down and you'll miss much of what's around you, but leave it too long and each new experience will push out the one before.
I've just returned from Florence. It was beautiful and I don't want to forget any of it, but if I'd tried to write down everything as it happened, I would only have done half as much. Instead, I tried to jot down keywords to jog my memory when I got back to the hotel later, and so far it appears to have worked. I have virtually a whole notepad full of sensations, places of interest, trattoria, people, art and all the ideas they provoked, and I'm still adding to it now that I'm home. Not only do I have a useful reference for features and fiction, but I have a better reminder of a great holiday than I would have by taking any number of snaps.
One other tip: if you think you might be writing features on your trip, don't only take notes and photos, keep any tickets and receipts as they'll have dates, names, locations, prices etc. that you can be sure are accurate.