With an extra pack of thread you won't have to worry about running out of thread in the middle of an important repair. Waxed polyester thread, available in packages of 180 yds. each.
When in the field, I keep several yards of this thread in a small pouch that also contains a variety of needles and other types of thread. During my last hunt, the seam above my heel ripped out and I had to sew it up with my emergency kit. The thread is still there and in good shape. If you don't carry the awl with you, make sure to carry a multipliers as well since the needles can't be pushed through leather without it.
The Speedy Stitcher is one of the most useful things I've got in my emergency kit. The only problem I've had is keeping enough thread on hand. I've used the Speedy Stitcher to create custom tarps, repair fan belts, and temporarily repair clothes while out hunting - mesquite thorns can tear tremendous holes in inadequate hunting gear! I highly recommend the Speedy Stitcher and this replacement thread spool to anyone needing quick and easy repairs and a creative tool.