It doesn't matter what sort of project you're doing—at one point or another, you're going to need a utility knife. With the Irwin Folding Utility Knife, you can always be ready. Besides the patented BladeLock technology that prevents mishaps, what contractors love most is that, integrated within the handle, there's a holder for backup blades. When one blade inevitably goes dull, you can speedily swap in the next and continue working. Available on Amazon; $20.87.