I would change my identity and move to Scotland. 

The next poster won a Lamborghini in a raffle 

I... would probably sell it. I'm not a big car person, so a car that fancy would probably be more trouble than it's worth. But I'd probably take the money and save it until my current car needs replacing.

The next poster is invited to go to a community theater by friends.

I'd go with them of course!

The next person discovers how to time travel.

I travel back in time, write an insane historical fiction novel, turn it into a bestselling series, make millions and retire in my 20s. 

The next person is told that the Matrix is real, and are offered the choice between a red pill and a blue pill (either wake up, or keep dreaming forever...neither is NOT an option).

I must be like Digory, because I find myself applying the logic of "if I take the blue pill, I'll go crazy wondering what would have happened if I'd taken the red pill" to this question. Red pill it is, then.

The next poster goes into their kitchen one morning to find a very extinct species of dinosaur very much alive and currently raiding their refrigerator.

Uh, honestly? I'd probably scream. After which point, I'd probably call the police or animal control or something. Just because it's an incredible find doesn't mean it's not dangerous!

The next poster wins $100,000 in a contest.

I’d use it to get through college! 

The next poster accidentally spills water on a celebrity.  

I would apologize profusely and then go hide in the restroom for a very long time.  

The next poster is left alone in a room with a wardrobe.

Oh, I am definitely climbing in and seeing where it takes me. But I wouldn't shut myself in, of course. 😉

The next poster unexpectedly has a day off from all responsibilities.

I’d finish embroidering my lions mane while watching Narnia and LOTR. 

The next poster discovers a group of outlaws meeting in the attic. 

I bake them imaginary cookies and tuck them into their toy box with the toy indians as well

The next poster finds that the Narnia Web forum has been updated ? 

... and goes "Wooohooooo!" on discovering it's even better and nicer that the old one!!  

The next poster finds him/herself in the Wood Between the Worlds.

Assuming I had the rings (or a similar means of travel), I'd do the same trick of marking the pool I came from and do some exploring. 😀

The next poster discovers a mysterious old book in an attic.

I'd spend several hours reading it before realizing I was about to be late for work. 😛

The next poster is given a magical bean by a mysterious old man in the woods.

I'd plant it and care for it as it grows, hoping it would lead to an adventure.

The next person finds a crashed UFO in the woods.