I would like to enchant something for my girlfriend. I would like it to be an enchantment of protection, or happiness, or well being. Something she can keep with her when I'm not around to give her strength and happiness
Aww, that's super sweet :) Necklaces are pretty handy and easy to take around everywhere, but just make sure she doesn't have any allergy to nickel or other faux metals or materials. If she's a purse girl, you could enchant a key ring ornament to put on the strap.
Really any jewelry would work well... I always wear an enchanted pendant on an inverted pentagram, an enchanted sphere of chaos pendant, and an enchanted ring... You could also... For practical protection, enchant a knife she could carry in her pocket or purse.
If you really wanted to, you could get one of the things others have suggested, but I would suggest with a crystal of some kind. Then you could cleanse it, then charge it with those certain tasks. Then if you really wanted to go over the top, you could carve runes into it somewhere for what you want.