Enjoy what you have when you have it. "Make hay while the sun shines".
Work is not the be-all and end-all. Take time to smell the roses. Realize that jobs are more often transitory, but work/career is something you need to do everyday. Owning excess things is not important, "you can't take it with you". Live within your means.
Be careful who you marry. Watch how others treat their existing friends before becoming their new friend. What a person does (their actions) is much more important than what they say.
Things that interest you now, may not interest you in the future or things you can do now you might not be able to do in the future. Do not say, “I will do that or I can do that next year.” Do it now or decide that you can live without doing it. Then if you get to do it fine, but if you can't do it, you have already made your peace with the idea.
Explore (even if it is just your neighbourhood, or your library), try new foods, experience as many new situations that present themselves, but balance what you do with down time. A dose of boredom will not kill you, and it might give you time to get some perspective.