Looking at your page in a mobile simulator, you could possibly do some quick CSS changes to improve this. Try playing around with the
.navbar-toggle + .head-search
style for the max-width property. I tweaked the max-width to 153px in the sim for an S3 and got the Login/Register buttons to be on the same line. If you find some CSS that works for you, you can also just target it at mobile devices with the @media (max-width:480px) tag.
Another thing you can try is changing the Login and Register buttons to be text links, instead of buttons.
-Melissa
SCLogin - Responsive
