Agree regarding the kennel advice above. We bought a second hand SkyKennel on Craigslist (maybe try this or Ebay local to you?) and while it would have been fine for the kitties based on our measurements, we decided in the end to stump up for the next size up at Petsmart to give them a bit more headroom and light. The LAST thing I wanted was to get to O'Hare and have to run around finding a new kennel. You don't want to go too big so that they are tossed around, but if you are on the edge of measurements, its better to be safe than sorry.
Kitty measurement and kennel worries took up a bunch of time, almost as much as timing and sorting out the vet paperwork.
Third on the Dryfur packets! We went that route too and were very pleased with the package and service. I also got some of the absorbant pads that were AMAZING - one of the cats had an accident in the crate or just couldn't hold it the whole way and I had no idea until two days later when I really checked the pad - no smell, no muss, nothing. We even had our two in the crate together (as per our airline's regulations - keep in mind ours flew SAS to Stockholm - not sure if any available airlines to the UK allow two pets in the same carrier, but you could check) and they came out nice and clean.