Today is Gonna Be a Great Day

 is the full version of the series' theme song. It is performed by the band Bowling for Soup. Most of the things mentioned in the second verse are actually done by Phineas and Ferb in season 1.

Lyrics
WwCRcTfFzkI There’s a hundred and four days of summer vacation, 'Til school comes along just to end it, So the annual problem for our generation, Is finding a good way to spend it Like maybe…

Building a rocket, or fighting a mummy, Or climbing up the Eiffel tower, Discovering something that doesn’t exist, Or giving a monkey a shower Surfing tidal waves, creating nanobots, Or locating Frankenstein’s brain, Finding a Dodo bird, painting a continent, Or driving our sister insane! This could possibly be the best day ever, (This could possibly be the best day ever) And the forecast says that tomorrow will likely be a million and six times better. So make every minute count, jump up, jump in, and seize the day, And let’s make sure that in every single possible way, Today is Gonna to Be a Great Day! Crossing the tundra or building a roller coaster. Skiing down a mountain of beans, Devising a system for remembering everything, Or synchronizing submarines. Racing chariots, taming tiger sharks, constructing a portal to Mars, Building a time machine, stretching a rubber tree, or wailing away on guitars. (Oh, man.) This could possibly be the best day ever,

And the forecast says that tomorrow will likely be a million and six times better. So make every minute count, jump up, jump in and seize the day, And let’s make sure that in every single possible way, Today is Gonna to Be a Great Day! Hey! Hey! Hey! Hey! Hey! Hey! Hey! Hey! Let’s put our heads together and design a master plan. We may miss dinner, but I know mom will understand… We got our mission and some pliers, yogurt, gumballs, and desire. And a pocket full of rubber bands, with manual on handstands, A unicycle, compass, and a camera that won't focus, And canteen full of soda. Grab a beach towel here we go! (This is Ferb-tastic) This could possibly be the best day ever, (This could possibly be the best day ever) And the forecast says that tomorrow will likely be a million and six times better, So make every minute count, jump up, jump in and seize the day, And let’s make sure that in every single possible way (Seriously, this is gonna be great) This could possibly be the best day ever (Today is Gonna be a Great Day) This could possibly be the best day ever Today is Gonna be a Great Day

Trivia
Most of the things said are used to make episode plots. These are the examples:


 * "Building a rocket" - Out to Launch


 * "Fighting a mummy" - Are You My Mummy?


 * "Surfing Tidal Waves" - Lawn Gnome Beach Party of Terror


 * "Creating Nanobots" - I, Brobot (Loosely, there are robots)
 * "Painting a continent" - Oil on Candace (The helicopters with paintbrushes)


 * "Driving our sister insane" - Almost every episode, unconditionally, though The Best Lazy Day Ever has a humorous and literal way.


 * "Skiin' down a mountain of beans" - S'Winter (Very Loosely (Snow Theme))


 * "Building a rollercoaster" - Rollercoaster


 * "Synchronizing submarines" - Voyage to the Bottom of Buford, ''Journey to the Center of Candace (There's a submarine)


 * "Racing chariots" - Greece Lightning


 * "Constructing a portal to Mars" - Unfair Science Fair & Unfair Science Fair Redux (Another Story)


 * "Building a time machine" - It's About Time!


 * "Stretching a rubber tree" - Tree to Get Ready


 * "Wailing away on guitars" - Flop Starz - Dude, We're Getting the Band Back Together (Guitars)


 * "Discovering something that doesn't exist" - The Lake Nose Monster

From Phineas and Ferb Wiki, a Wikia wiki.