For jobsite use, there’s nothing like a good utility knife. They’re sturdier (and arguably safer) than folding knives, and much more functional than fixed blades. We prefer the Stanley 10-499 QuickChange utility knife.
While it won’t win you any style points and isn’t nearly as fun to use as a folder, the 10-499 is easy to use and a very handy tool in construction settings. Particularly effective when wearing heavy gloves (like the Mechanix Material4X gloves), the 10-499’s blade storage is sufficient and its quick change feature is easy to use.