I would only use your charms on a peice of armour that you think you will keep till the end...once out in - you can't remove them.
Lockpick - yes worth it - to get a piece of the map, you will need it.
Spells - Life Leech - i used it on huge bosses (gragons, the guardian of the eye of the cyclops)
Elemental Hail is good. As well as Hell spikes.
Though everyone has thier own opinions. But these i used straight till the end.
