If for some reason you have to do a group project for school and in order to complete that project you must buy supplies, make sure that all group members are present during that process. For if you don’t you will feel the need to include the third member in the group due to their absence. Therefore you will call that group member and in order for you and your present partner to both be able to hear that person the phone will be put on speaker. This results in you and your friend trapsing around Wal-Mart yelling into a phone as you frantically attempt to find all necessary supplies in a timely manner while the other shoppers give you strange looks.
Quick Summary: Make sure that all group members are available for all parts of a project.