This is the perfect time to learn how to do a buttonhole. There's a video for one simple buttonhole here
. You can make the buttonhole over as many sts as you like, depending on the size of your buttons (and remember that knitting is very stretchy so the buttonhole should be slightly smaller than the button). There's a prettier, but more complicated buttonhole on this website under the Free Videos tab at the top of the page, Advanced Techniques.
I love learning something new with every project. Enjoy knitting the scarf!