In reply to Philip:
I would go with a standard rack and a couple of large, simple but budget panniers. You should be able to simply drop small, lightweight rucksacs (KIMM sacs) straight in, together with any extra clothes you don't want to wear cycling, etc. Have a couple of bungees with you in case any extra shopping, souvenirs, beach combing relics (whale bones) need to be taken home.
Empty panniers can be left on the bikes as they are no more attractive than nicking the whole bike is already. You can take an extra small thin cable to thread through the straps to stop scallywags simply lifting the panniers off and away for the devilment. Alternatively the judicial use of a couple of cable ties makes nicking them more of a hassle. Secondhand / budget panniers also makes them less desirable and more easily replaced.