Luggage

[RizzoTheRat]

The Mrs uses her (ancient heap of a) bike to cycle about 5 miles each way to work, and is finding carrying a small rucksack is starting to hurt her back.

I was thinking a rear rack and panniers would be the sensible option, but I then noticed you can get rear baskets for less money than a rack. Anyone know if these are actually any good or just really flimsy? eg
http://www.halfords.com/webapp/wcs/stores/servlet/...
or
http://www.evanscycles.com/products/adie/large-rea... (plus another tenner for the support arms to the rear axle

Otherwise what should I be looking for to carry around 15-20 litres bearing in mind she doesn't have a rack already?

[Fourmotion]

I'd check firstly whether her bike has eyelets to hold a rack - if not then it rules out a pannier straight away.

Can't help with the basket, although I'd think you'd need to strap down whatever you had in there, and it would need to either be covered or waterproof itself.