BTS Theme
It depends on the grade you teach, but when I think BTS, I think of apples. It also fits in with September and Johnny Appleseed. I did my room in stars and have kept it up all year. I am planning on a castle/knight theme next year. You could also archive various themes and see which one suits your taste and budget. For my stars, I have stars hanging from the ceiling. I also have some stars on my door and cabinets. I have star borders and have made the headings on my b-board something involving stars. I have one of those 9 or 10 feet posters about stars. My Math Wizards board has stars. It was something simple for me to plan and fit my budget. Our school's mascot is stars as well. I just didn't keep it limited to patriotic colors. My word wall has large stars with the letters and smaller stars with the words on it.