Bag holes

Be sure to check a plastic grocery bag for holes before it's used to contain something wet and drippy, even if the bag is new from the store.

iTunes auto-check box

Command-clicking the "check mark" boxes in iTunes will check all/none automatically.

Oil/cars

If you're going to check your oil in your car, drive the car for a mile so that the oil is at a performance level when you check it; if you check oil without having recently driven you'll inaccurately read the level.