Students often struggle with dimensional analysis (factor labeling). What they need is practice, but not dull and tedious practice with units that don't mean anything to them. This activity gives them plenty of practice in a cooperative setting, using a real world application, and it's easy for you to grade. Students turn in a shopping list at the end of the activity and you just check their quantities. This activity works well with all levels of chemistry and physics.
Keywords: dimensional analysis, factor label, train track, precision, accuracy, significant digit, figure, error, chemistry, physics, metric