Lol, sewing needles and thread. Sewing machines won't work if they don't have electricity to run them. And torn clothes aren't much fun in cold weather. And get some of the ones with large 'eyes', too. If the need should arise, you can use them to 'repair' your footwear.
Get a packet of leather ones with a point that pierce, some curved upholstery ones, some long ones, some big eye ones, and some tapestry blunt ones for repairing knit wear (socks). Don't forget a thimble. I find the cheap plastic ones to be the best, actually. Whatever it is, it should have good divets. If you DO forget the thimble, and you are working on leather or canvas, use a spoon. Needle nose pliers will also help pull a needle through leather or canvas.
If you don't already knit, ask a friend for a spare ball of yarn (synthetic is good for sock repairs). The repair doesn't have to be pretty, or "correct," you just want to contain the damage and replace the lost fabric.
On a similar topic - a couple packets of extra boot laces.
ETA: One last thing: This may be controversial, but I've used it many a time with success (lots of hiking, and also planting trees for a company)
duct tape. Use it directly on the skin BEFORE you get the blister (and, NEVER pop a blister). I've wrapped my feet and hands, depending. It protects.