Heres a list:
1. Favor from your worshipped gods/god.
2. General health ( a person who is healthier will be able to focus better and use more energy )
3. Herbs ( especialy those which are burnt for trance induction purposes )
4. Specific Minerals , Semi-precious and precious stones (such as amethyst)
5. Phases of the moon
6. Equinoxes and Solstices
7. Alignments of cosmic bodies ( such as planet alignments )
8. Specific holidays of any origin ( most people say that Samhain also known halloween is the best )
9. Specific spells and rites to imbue an object with energy which could later be used
10. A sacred or powerful area such as temples or forest groves
Hope that helps you some , if you have anything to ask feel free to mail me.