Mark, it all depends on your level of pride. I'm sure there was a plastic bag in your luggage, if only the hotel laundry ones (as far as I can see the only use of these is to keep your dirty stuff polluting your clean stuff - does anyone pay £10 for a short to be cleaned?). Get it out, fill with 6 kilos of stuff. This is now your "carry on" bag.
There is no rule that it has to be pretty.