If you go to the Carpet Capers level on story mode, you can get 1000 coins and an easter egg. In this level you will find a tower with an enemy whose name is Egg. Go through a hole which is at the bottom of that tower and pick up a jewel. Then you will see a message that says that you have found an egg. Now you can finish this level.
In the Escape From Three Rex on story mode, go down to the crate which is on the platform. Get this crate to receive bazookas. If you make a shot at the mouth of the T-Rex, you will accomplish this mission and will get 1000 coins.
Go down to the cliff (where's the professor) in the Nice to Siege You level on story mode. Then you have to go inside where the entrance is, thus you will be able to see a worm looking like a rabbit. Finish the level and get your 1000 coins!
In the Tin Can Alley level on story mode, take a look around and shoot at the toilet. Since then the level will be completed and you will get points and an easter egg.
Blow up a car in the mission called Destruct and Serve. To be able to do this you have to possess an explosive weapon. If done, you will receive 1000 coins and an easter egg.