For minor holes, there is no sense in filling them with putty or going through elaborate repairs, but they still need to be filled in to avoid those little marks all over the walls. One of the easiest and least expensive ways to do this is by using plain white toothpaste.
Plain white toothpaste is getting harder to find these days, with all the special features of modern toothpaste (what happened to simplicity?), but you can still buy a tube at most stores.
Using a toothpick or other small object, gather some toothpaste and force it into the hole. Put enough in there to completely fill the hole, and then scrape off the excess to make it flush with the wall. You can even use the toothpick to make texture in the toothpaste.
While it will not restore the wall, it will restore its looks. Once dry, a hole filled with toothpaste will look almost invisible, at least on a white wall. If your walls are not white, you will need to cover over the fill job with paint to match.
Toothpaste is a cheap fix that will get your walls looking great again with very little time or effort.