Hammer and Nails
If you had a hammer, would you hammer in the morning? Maybe a better question to ask is what do you do when you don't have a hammer? While hammers come in all shapes and sizes, the claw hammer is the one most of us know. It's a handy item to have -- with one tool you can pound nails into wood or use the claw end to remove them. It's hard to imagine any construction job that wouldn't require a hammer and nails.
Other hammers are equally useful. You might need a sledgehammer when tearing apart a structure. Rubber mallets are useful when you need to strike a surface without damaging it, and ball-peen hammers are good for metal-working jobs. But for your basic hammer needs, the claw hammer is hard to beat.
Sure, you could always invest in a nail gun. But what do you do when you need to remove a nail? Sometimes the best tool for a job is the low-tech option.