I've done a bit of travelling this summer, from St Louis to the East Coast and back, and up to Chicago for a weekend. I've always been told that as a writer, I should keep a journal, but I thought that was just to write down story ideas as they came. I was wrong, partly.
I brought my writer's journal with me on my trips and a few story ideas came but it wasn't until I was out on the ocean that I realized another use for my journal -- to write down impressions (using as many senses as possible) of my experiences. Later that evening I tried to recreate what I had experienced, but I know I probably missed some important details. What a rich source of material I could have had...the North Carolina Beachfront, the seafood, the fishermen preparing their boat and all of the related sights, sounds and smells. Who knows when I might want to set a story in Calabash, NC or the Museum of Science and Industry in Chicago?
I may have missed something on that trip but I'll tell you what: my writer's journal is never very far from my side.