Today is Gonna Be a Great Day

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

Lyrics
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 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 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've got our mission and some pliers, yogurt, gumballs, and desire. And a pocket full of rubber bands, the manual on handstands, A unicycle, compass, and a camera that won't focus, And a 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, either directly or by a more loosely-based exploration of the idea:


 * "Building a rocket" - "Out to Launch"(building it to see thier star)


 * "Fighting a mummy" - "Are You My Mummy? (really candace)


 * "Discovering somthing that doesn't exsit" - The Lake Nose Monster, Fireside Girl Jamboree (this is referenced in the song Go Candace Go)."


 * "Giving a monkey a shower" - "Swiss Family Phineas" (Ferb specifically says, "Yep, had to be done.")


 * "Surfing tidal waves" - "Lawn Gnome Beach Party of Terror" (surfing, but not on tidal waves)


 * "Creating Nanobots" - "I, Brobot" (robots, but not nanobots).


 * "Locating Frankenstein's brain" - "The Monster of Phineas-n-Ferbenstein" (not really frankenstien's, but a giant platypus who resembles him!)


 * "Painting a continent" - "Oil on Candace" (the helicopters with paintbrushes paint a desert)


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


 * "Crossing the tundra" - "S'Winter" (Candace enlists Buford's help to pull her on a sled up the mountain.)


 * "Building a rollercoaster" - "Rollercoaster"


 * "Skiing down a mountain of beans" - "S'Winter" (skiing on snow instead of beans)


 * "Devising a system..." - "Gaming the System" (they make an advanced version of Jump and Duck)


 * "Synchronizing submarines" - "Voyage to the Bottom of Buford" and "Journey to the Center of Candace" (submarines appear in both episodes)


 * "Racing chariots" - "Greece Lightning"


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


 * "Building a time machine" - "It's About Time!" and "Phineas and Ferb's Quantum Boogaloo"


 * "Wailing away on guitars" - "Flop Starz", "Dude, We're Getting the Band Back Together", "Tip of the Day", "Oh, There You Are, Perry", "The Baljeatles", and "Phineas and Ferb's Quantum Boogaloo".

The episode "Phineas and Ferb's Quantum Boogaloo" shows more literal examples of the Big Ideas described in the song:

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 * Skiing down a mountain of beans
 * Devising a system for remembering everything
 * Taming tiger sharks
 * Stretching a rubber tree

Two final Big Ideas have not yet been shown in any fashion:


 * Climbing up the Eiffel tower - Assumed to take place during an episode called "Paris Panic", which has since been confirmed as a fake episode. However, it should be noted that at the beginning of "Voyage to the Bottom of Buford", Ferb is atop a scale model Eiffel Tower constructed of sand. and in "Rollercoaster" they land on it.


 * Finding a dodo bird - Not attempted yet, but since in "Phineas and Ferb's Quantum Boogaloo" they expressly stated that they will never again go in the future, they just might go in the past when they do attempt it.