Daypack - Carry a small backpack or security purse with your daily needs. NOTE: Anything on the list below that is liquid should be packed in your main, checked bag for the flight to avoid running afoul of TSA regulations about carrying liquids over 3 oz.
Swiss Army Knife - or a Leatherman/multitool. Most useful features: screwdriver/can opener, blade, corkscrew (for picnics), tweezers, scissors, nail file. Note: The TSA has been debating allowing small knives in carry-ons again—though HAS NOT YET changed the rules. For now, pack any knife in your checked luggage.(Official TSA regs)
Everyone knows Brits drive on the left side of the road—except for on one road in London. Savoy Court—the driveway off the Strand up to the entrance to the Savoy Hotel—is the only right-drive road in the U.K.