| This is very true, and extends beyond such obvious dual-purpose items as kitchen knives and entrenching tools.
Anyone who has ever seen a bar fight, be it in a movie or in real life, knows that any relatively heavy, hard, sharp, or pointy inanimate object can be used to bludgeon, strike, impale, or cut an opponent. (This also applies to kids playing in a sandbox.)
Hand tools make excellent weapons, and if they are powered, even better. Screwdrivers, hammers, staple guns, pliers, T-squares, pipe cutters, and other miscellaneous gear can not only be used as melee weapons, they make handy (pardon the pun) interrogation tools. Powered, bladed devices such as chainsaws and gardening machinery are so freaking dangerous in general they don't even really count as improvised weaponry.
Heavy construction equipment makes for dandy siege weaponry and armored vehicles. Again, this is a category of machinery that can't really be considered impromptu, as any combat engineer will tell you.
The Kitchen is full of deadly stuff far beyond the simplicity of blades, bludgeons, and other means of eviscerating, pinching, basting, or filleting an enemy. The really scary stuff under the sink can kill in ways too horrible to mention. Just ask someone who ever accidentally mixed the wrong cleaning fluids together, or a cop who has ever raided a tenement on the danger of lye as a weapon.
If you saw the movie Casino, Joe Peschi proved that the pen is not only mightier than the sword; it can make a grown man cry.
Glass falls into a special category entirely.
Guitars are another special-case scenario, as Quick-Draw McGraw as "EL Kabong" has all too often in the past demonstrated the effectiveness of stringed instruments as a weapon to fight evil. (Woody Guthrie is also known for this.)
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