Already answered by many posters here, firstly the crew member may be away from home for longer than you think. Especially US East coast flights which are usually linked so part of a 6 or 7 day trip. They may be commuters from somewhere who leave home a day or more before their trip leaves.

Crew are also not sure what they might need, standby could mean summer in Sydney or Winter in New York. They also may need a spare set of stuff for travelling home as a passenger.

Oh and YES they may well be wanting to do some shopping...... and why not! And also depending on destination, some comfort items to make them feel at home, kettle, food, snacks, books, DVDs, or indeed they may have got stuck in an ash cloud with no spare knickers so are being cautious!

I once did a Nairobi nightstop with a carry on bag only, and ended up being away for 19 days! Never again will I pack to the minimum!