Greetings @amara,
You’ve got some great advice about offerings here! It really does depend a lot on the traditions of the witch as well as which deity they want to make an offering for. Different deities have different preferences- if you search for the diety on Spells8 or check out the Temple of the Goddess Course, individual deities have their own pages that list recommended offerings 
There’s also a great guide about Making Offerings at Home and this discussion about Help with Offerings that has lots of advice and suggestions 
Wishing you all the best with your offerings, Amara- blessed be! 