Buzzfeed has broken down the biggest regrets. A few being:

1. Not traveling when you had the chance.
2. Missing the chance to see your favorite musicians.
3. Staying in a bad relationship.
4. Caring too much about what other people think.
5. Not stopping enough to appreciate the moment.

See those & More:
http://www.buzzfeed.com/mikespohr/37-things-youll-regret-when-youre-old