You can do this as a whole group activity and jot down UP phrases as your students think of them, making one poster, or use this as an interesting activity for your Daily 5 word work and have students each make up their own.
After reading Seuss's book, Great Day For UP! challenge students to think up as many phrases that end with the word up. Can they think of some for each letter of the alphabet? I came up with 222, but had no words for i, q and x. (U of course could simply be up.)
Give students a choice of 4 different UP posters that they can write their words on. For a cute bulletin board, I've also included large U and P letters. Run off on a variety of colors of construction paper. Students cut them out and then glue to another color of construction paper.