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
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 suppliers, 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 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"


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


 * "Discovering something that doesn't exist" - "The Lake Nose Monster"
 * "Giving a monkey a shower" - "Swiss Family Phineas"


 * "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" - In "The Monster of Phineas-n-Ferbenstein"
 * "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"
 * "Taming tiger sharks" - Possibly "Backyard Aquarium".


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


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


 * "Stretching a rubber tree" - "Tree to Get Ready" (the trees are transformed and stretched into tree house robots)


 * "Wailing away on guitars" - "Flop Starz", "Dude, We're Getting the Band Back Together", and "Tip of the Day"

Some people have assumed that because a few of the things named in the song have appeared in the episodes, that all of them would appear in an episode. Below is the list of Big Ideas from the song that have not been shown in an episode:


 * "Climbing up the Eiffel tower" - Assumed to take place during an episode called "Paris Panic", which has since been confirmed as a fake episode.


 * "Finding a dodo bird" - Not attempted yet.


 * "Devising a system for remembering everything" - Not attempted yet, although Phineas and Ferb have devised a system as seen above.