Last year I bought a very useful detachable rear basket for Petunia, which looks even better on Penelope. It's plastic wicker, with a handle so you can detach it and carry it into the shops. The handle has an unfortunate habit of bouncing from the back of the basket to the front and when I'm on Petunia, whose luggage rack slopes towards the saddle, hits me on the backside.
Penelope's luggage rack is nice and flat, so the basket itself stays where you put it instead of sliding forward, and if the handle bounces my bum is well forward of it anyway.
Below is a closeup of how it attaches - you simply pull handles on each side underneath to compress the springs, and let go so it grips on. It's a neat little unit, weighs a kilo and a bit, carries quite a lot and is very stable. Sadly there's no cover on the top, so I usually put an eco shopping bag inside and tie the handles together to stop anything bouncing out.
The basket cost me $39 on eBay. I've seen them for more in the shops, even allowing for eBay postage.
Today was the first time I've needed to put the rear basket on Penelope, and she carried a good load of fruit, veg and meat back from the shops. I hardly noticed the basket was there despite the extra weight - she is so lovely to ride!
My husband doesn't have any racks on his bike - a smug 12kg road bike with no mudguards - so carries his load in a backpack as he did today. Even if we fitted racks to his bike I can't quite see him with a twee basket like mine :-). Might have to persuade him to fit racks and buy panniers, so we can shop by bike more often and do most of the grocery load that way.