"To Do Today" is a very short song sung by Dr. Doofenshmirtz in "Last Day of Summer"
Doofenshmirtz: to-do to-day, to-do to-day.
Doofenshmirtz: It's like a little song!
Vanessa: (angrily) Dad!!
Doofenshmirtz: to-do, to-do to-day, to-do,
Vanessa: (rolling her eyes) Ugh! (walks away)
Doofenshmirtz: to-do todaaay!
All the ladies in the house say— (points where Vanessa was) Wait! Where'd she go?
"Evil Jingle" ("Last Day of Summer")
"There's No One I'd Rather Go Nowhere With"