Not sure if you mean to strap to the machine, or to carry with you for backup lighting.
If it is for backup lighting, and you are carrying it strapped to the machine, or in a storage compartment on the machine, make sure what ever light you have is seriously shock protected in foam. The jarring will beat the crap out of most anything on a long haul.
I would go for Surefires myself. I've had a couple beaten pretty badly, that the contacts just wore off from the batteries hammering them constantly.
I now carry anything electronic in pockets or backpacks.
If you are stranded, duct taping pretty much any decent light to the front will get you out of a jam.