I've done a variety of containers for entities, some following traditions, some following inspiration, some a combo. In your situation I'd do what you are already doing. Listen. Do divination. Dream. Feel. Let the project(s) develop slowly and with the guidance of the spirits you are working with. If they want xyz in the box or cauldron or whatever, then talk to them about it and see if they can provide it, accept a substitute, or accept a symbol. (ie sometimes you can use an image of something in place of the actual thing, a feather from a bird in place of the whole bird, and so on).
You shouldn't have to violate your morals or values to make things - if you do, then think twice about working with that spirit or why you have those values. In my own view, working with spirits is a group project and everything is negotiable. I'm not obligated to run around being their servant and fetching whatever they ask for. Nor will I treat them like slaves, either. It's a business partnership, sometimes a close and longlasting one, sometimes one that develops deep loyalties. Not everyone comes at it from that view, but in case it's useful to you, there it is.