Draw or paint 25 different vertical lines. Vertical lines go up and down. Start each line at the top of the page and go all the way to the bottom. Make sure every line is different. Make thin lines, thick lines, curvy, dotted, decorated lines. Make them colorful using whatever medium you'd like--colored pencil, crayon, marker, paint, even glitter!
Open your journal to an empty page. Using watercolors, paint random blobs of color all over the page. If the opposite page is also empty, you can make this into a two page spread. You might want to put something under the page if you don't want the paint to soak through to the next page. But if it does, that's kind of cool too! Let it dry before closing your journal.
One day, when you need something relaxing to do, use a black pen or thin black marker to make each paint blob into something different.