When it’s a heavy-duty sheath knife, mounted in the footwell of your car. This is a vintage 1980s advertisement for a Puma “Auto Knife” with its special-purpose car sheath.
This kind of blade carry is illegal in more than a few jurisdictions (mine included) and I’d probably have serious reservations about doing it anyway. Leaving a useful-looking allzweckmesser in plain view in your car is both an invitation to theft and to curious/alarmed law enforcement inquiries.
By the most odd coincidence I recognized the knife in these old ads, because the exact same knife lived in the glovebox of my buddy’s pickup truck in high school. The blade is exceptionally thick and weighted toward the point. It’s great for chopping and batoning, and it’s damned-near impossible to snap off the tip.
Leo’s truck knife was a dull, pitted beater (kind of like his truck) but you should keep an eye out for them at pawn shops: a Puma like this will bring $250 or more in good condition today.