When traveling in the UK, always pack a pair of trousers. Pants are underwear. Do not confuse the two.
I call trousers my pants and the "pants" my undies. I am pretty common though.
We understand what you mean by "underwear" and "pants" as well.
A trip to London is a good first trip out of country. Like you said, they speak English, and there isn't that much culture shock. "WC" means "water closet" and its the restroom, breakfasts are weird, the Indian food is awesome, and they really like this old woman with a crown.
Restrooms are Toilets, Breakfast is weird? Depends on where you go, and yes...Indian/Bangladeshi food is awesome and pretty common here.
I am guessing you have met Royalists (who are into the whole Royalty business), you won't meet as many Royalists in any other part of the UK though.
For countryside, just visit Wales. It's cheaper and you can climb Snowdonia if you feel like it.
I'll probably visit America one time in my life. My cousin is currently in New Jersey, teaching Americans "Soccer", since he wants to be a Fitness Coach. Which would suit him being in America, where the regime is a lot more tougher than in the UK.
I've also visited Jamaica (I guess for heritage reasons, being part Jamaican). My advice for that place is to be careful in shopping centres in Jamaica...they will badger you a lot, asking for money for things you don't want, and will even resort to shady tactics like putting items in your bag, unnoticed and carving your name into wooden Sculptures....so DON'T EVER MENTION YOUR NAME!
I actually "celebrated" Thanksgiving in Jamaica too (the only time I ever will), man...you guys have a lot of food! Even more than we do!?! If you visit the UK on the 5th November, we have a celebration called "Guy Fawkes" (We also call it Bonfire Night), to which we celebrate killing the Traitor who almost blew up the Prime Minister with Gunpowder...so it's like Independance Day, only the Fireworks are lit at night, and you usually have some festival going on in the towns around you where you eat barbecued burgers and Sausages (We're probably the only country to do this in the cold weather, LOL). The towns and places are usually VERY foggy around this time too due to the fireworks being fired off every 10 minutes. In fact, our Bonfire Night can concede with Halloween. (we have a rhyme at Halloween which isn't used in America, to which we reference "stealing garden gates" which references using them for Bonfires).
Sorry for the rant.