Here is a helpful tip that I picked up from Christa Quilts while watching her tutorial on Herringbone Quilts.
"Use up your left over bobbins, especially if they are cotton, when you are piecing a colorful Scrappy quilt."
Whenever I ran out of bobbin thread, I would always stop, unthread my machine and wind a couple of bobbins. Even though I use Bobbin thread, which tends to go for longer miles, I had never thought about using up the leftover bobbin thread. Now, maybe I am late on this tip, but I really like that I can use up bobbin thread and just keep sewing.
The bobbin thread that I have been using and like the most is The Bottom Line.
I have also used Sulky Bobbin thread and Madera. I find that I can sew for so much longer using these top quality Bobbin threads. And who doesn't want to just keep sewing :-)