I found a list once with offerings for specific deities. Hopefully this is of some help to you, but as suggested you may wish to research the deity in question and find out their qualities and associated offerings. You could also use your intuition when deciding on a offering to him or her.
Offerings to Specific Goddesses:
Aphrodite: olive, cinnamon, daisy, iris, and apple
Artemis: cedar, hazel, willow, daisy, and cypress
Astarte: alder, pine, cypress, myrtle, and juniper
Athena: olive and apple
Bast: catnip and vervain
Bellona: belladonna *Caution* - this herb is poisonous and should not be injected or handles without protective clothing.
Cardea: hawthorn, bean, arbutus
Ceres: Willow, wheat, bay, pomegranate, poppy, leek, and narcissus
Cybele: oak, myrrh, and pine
Demeter: wheat, barley, rose, pomegranate, bean, poppy, and all cultivated crops
Diana: birch, willow, wormwood, hazel, beech, fir, apple, and mulberry
Freya: cowslip, daisy, primrose, strawberry, and mistletoe
Hathor: myrtle, sycamore, grape, coriander, and rose
Hecate: willow, yew, mint, cypress, date palm, sesame, dandelion, garlic, oak, and onion