10-mL graduated cylinder
A graduated cylinder.
If it's a solid multiply the length times the width times the height. If it's a liquid use a graduated cylinder If it's an irregular solid drop it into a beaker, flask, graduated cylinder, or any other water-measuring tool and record how much the water goes up from the original height to the height when the irregular solid was dropped in, and subtract.
To find the volume of a solid you can't simply calculate, get a large tub of water in which you can completely immerse the solid. Fill the tub with water to the edge, then submerge the solid. Any water that spills over has been replaced by the solid and signifies the amount of space the solid is now taking up. Weigh the water or put it in 1l bottles. 1kg of water is 1l and a liter is a cubic decimeter. From there you can calculate the volume in any unit you want.
A ruler to find the measures of the edges and a brain to multiply them together.
A container of liquid in which to immerse the shape.
A ruler or tape measure.
If you can somehow describe the shape, a popular tool is integration. This means that you imagine cutting the object into thin slices, calculate the volume of each slice, then add everything up.(And if the slices have an irregular shape, they, in turn, are cut into thin strips - so you would be using a double integral.)
A metric ruler would be the best bet. Simply measure the length, the width and the height of the box and multiple all three measurements together to find the volume of the box in the unit that you measured the boxes in, cubed.
I would use a graduated cylinder or beaker filled part-way with distilled water. By measuring the difference in the height of the water column before and after inserting the object, I would be able to calculate the volume of the object.
mearing cup
Ruler
A graduated cylinder