Screwdrivers, must of bought over 600 screwdrivers( I am not kidding) motorcyle tie down straps, gas cans(I have no idea where they dissapear too) , crecent wrenches and vice grips and battery chargers.
For me its 12mm sockets, needle-nose pliers, and small flat blade screwdrivers. And general purpose rope. I buy rope probably once a month and never have a clue where it ends up.