2. KT Tape is a miracle product for sore feet, shins, knees, whatever. Keep it in your travel bag. Learn the right stretch ratios for different achy parts. It's lightweight and packs flat. Get the kind that lasts more than a day. Don't worry about the residue on your skin.
3. The Underground is really a neat transit system. Riding the Tube is fun when you understand it, and makes you feel like you're in control of your own destiny and transportation. Get the big Tube map and hoard that thing.
4. Print Google maps (street level) of all the area around your hotel so that you don't get lost and walk an extra long way back to your hotel without knowing where you are. Keep maps on you while you're moving around. I printed some great street maps of the Watford neighborhood, but then forgot to take them out of my travel journal when I left the hotel. :D. Rookie mistake.
5. People will scorn you for being a geek with a bunch of maps, until they're lost late at night and want to go home. Then they will want to know why your map of central London streets isn't helpful in late night Watford. Lol
6. Visit grocery stores for local snacks. You won't regret it. They won't bite you. (And you'll probably need some extra fuel if their continental breakfast isn't sufficient. We stayed in a chain hotel, so that's why the lame brekkie. I'm sure real English people eat better breakfasts.). Sometimes they have a laugh about hearing your weird accent.
7. You haven't gotten the message about the water and the coffee yet? Hey, why don't you find a takeaway coffee shop and have an afternoon caffeine boost? :). Trust me!
8. Nobody is concerned with your pants being unwashed between wearings. They don't care as long as you smell and look clean.
9. Make sure your traveling chewing gum doesn't have Xylitol in it. You don't want that kind of problem for half of your trip.
10. Don't exchange dollars for euros at English train stations and airports. You'll get charged double exchange fees. It's better to just go to an ATM when you get to the country that uses euros. And make sure you have some cash -- credit card fees will kill you if you use one for every purchase.
11. Cornish pasties are SO amazingly delicious, but your travel group will be afraid to try them, and opt for McDonald's and KFC instead...
12. If you are trapped at Heathrow, and you're sick, you're out of luck finding cold or allergy medicine and you should hit the only duty free shop you will be allowed to pass on the way to your shuttle, and buy a bottle of whiskey to knock your sickly self out.
13. They're really paranoid about immigration at Heathrow. Make sure you have the name of the hotel where you'll be staying and can prove you're not trying to sneak in and become an English citizen.