Either grams or kilograms - depending on the size of the potato.
As a potato chip is light weight I would use grams and milligrams.
Normally pounds or Kilograms but larger amounts could move in to tons and metric tons
The weight of a potato would best be measured in grams.
You would use the metric unit "liters" to measure the capacity of a hot water tank.
1 US gallon = 3.78541178 liters. Only if you mean pure water, then 1000 litres of water weighs 1 metric tonne. 1000 litres of water are 264.172052357 gallons that weigh 1 metric tonne.
You would use kilograms (kg) to measure someone's mass in metric units.
Metres
You would typically use the metric unit of centimeters to measure the growth of your hair.
You would use liters (L) to measure the volume of a soda container in the metric system.
You would use the metric unit "kilograms" to measure the weight of a bag of groceries.
Potatoes are sold by the kilogram.
A thermometer.