Rachel chastises her sister for going shopping instead of looking for a job to support herself, but Rachel did the exact same thing in the first episode. Both of them even named their purchases based on their situations ("Don't you want to rent me this apartment" pants).
One of the reasons why Phoebe counts the Friends when Jill knocks at the door is because in many cases one of the Friends isn't with the remaining five. They are usually at work or on a date.