Boot laces always break at the least convenient moment, if there is such a thing. It's just one of those things, like toast always falling butter-side down. Happily, they're easy to change and a fresh pair doesn't cost much. Replacement boot laces are cheap and light so any hiker can have a pair at the bottom of their backpack ready for quick deployment. It might not be your laces that snap at the wrong moment but handing a replacement pair to a stranger on the trail will make you an instant friend (so maybe buy a few extra for swaps!)
Nathan Trail Lock Laces 1162N
Shoe Gear Alpine Boot Laces - 72 in 375102
A handy boot lace can also be used as a guy rope on a windy night, as an emergency dog leash, to tie a sleeping bag into a broken stuff sack, or to secure a splint in an emergency. They can be used to practice rock climbing and fishing knots, to keep a bag of food high up and out of reach of hungry animals, or for a thousand and one other backwoods tasks.