I don't have a computer, so I've been using someone else's to do the software upgrades to my iPhone 4. Later this year, I'm getting my own computer. I want to delete my iTunes on his computer and put on my computer (when I get it). I'm scared I will lose my music, movies, and apps. And what if I want to give him some of my songs as a thank you? I don't want to lose anything.
iTunes media can be simply copied to another drive and restored at leisure.
As for leaving gifts behind, iTunes' music has been DRM-free for a pretty long time now, so you should just be able to copy the files between machines. Be aware that they are still traceable to you — if your friend starts distributing them, you could get in trouble.