There are some items from lower-level quests. quite handy at endgame, that haven't been given a target level or zone restriction. So when leveling it wouldn't be a bad idea to tuck them away in the bank for tough situations later on. Here's what i've found:
Bag of Marbles
Really Sticky Glue
Glowing Wax Stick
If i recall corectly there was also a 8 sec invulnerability potion from a quest in Ashenvale or Feralas, can't quite remember. If you know more, share them so i can keep up a sort of a list.