Hm, this is kinda tough. I feel that after I wished, I'd think of other things to wish for...
How about
1. Be psychic (includes clairvoyance, Telepathy, E.S.P. etc all of them^^) Then I could teleport all of the first nations unwanted food to third world countries and, bada boom bada bing, no more world hunger) (not to mention I'd be able to make a living tell fortunes and contacting dead loved ones^^) Also, inducing hallucinations, so people could meet their fav characters or dead loved ones, or enter their fav story.
2. End organized religion. Seriously, this is the cause of more disagrements and wars nowadays. Not ending religion, people will still be free to practice whatever religion they desire, but there will be no more segregation between religions like going to a mosque or church.
3. End prejudice. Probably not all at once, but speed up the process^^
Hopefully, once the world is all friendly and happy, we'll be able to cooperate and make as many scientific advancements as per needed with our growing population and climate concerns^^.
(Yeah, no world peace, we have to learn to achieve that on our own)