Casting a circle to demark a sacred space is all about the environment, time, people involved, and magickal workings afoot, in my opinion. Some witches will tell you it has to be marked in a certain material or the circle will fail. Feel free to look these people in the eye and call bullshit!
During our time, we have used, salt, holy water, incense, personal power, group power, the coven sword, athame, cord, flowers, hubby’s lasso (don’t ask, please!) chalk, chants, singing, bells and drums, essential oils, stones, tiki torches and so much more. You mention it and we have more than likely tried it or will try it in the future.
Each medium we have used thus far worked. Some can be used anywhere, though some work better for strictly indoor or outdoor use, but all do work.
If there is a unique situation, such as spell work to insure a good harvest, working a circle outdoors is best and you may use flour, cornmeal, or other food products, nuts, seeds, etc. A few points I would ask you to remember is that outdoor work means that you have to consider the elements. Flour and cornmeal blow in the wind quite easily ending up with more on robes and in eyes than on the ground. Some foodstuffs will draw every ant in the vicinity. Trust the voice of experience on this one, a circle of ants is no fun at all. Some seeds will end up as permanent living additions to the space if you are not careful. Rocks work well outdoors, as do tiki torches. For a handfasting or betrothal, I suggest using local wildflowers picked specially for the event, as they are beautiful, festive and add sweet scents to the occasion.
Outdoors around treed areas where you may need something easy to see during nighttime rituals, I suggest white cotton cording as it is easy to spot in moonlight, torchlight, and candle light. If you want to help the trees at the same time, you can use Epsom salts, as they are larger and easier to spot amongst the grass. When it rains or if you water the Epsom salts into the soil well, they provide a good source of nutrients for the trees as long as you are not too heavy handed with the salts or do not do more than two or three rituals a year in the same area. Space it out between rituals if you are a frequent outdoors group or person, as too much of even a good thing can cause damage.
Indoors, depending upon the flooring, you may choose to sprinkle holy water, lightly, from a rosemary branch. If you are concerned with wet floors and slippage as on ceramic tiles, vinyl flooring, etc. you might want to work with personal power gathered in from your core and sent to the floor via finger or athame, or appropriately scented incense for the occasion.
In carpeted areas indoors, using plain chalk or baking soda with a few drops of a targeted essential oil blended in well can be easy to put down and easy to remove. The latter even leave your carpet smelling better than before the spell. I would suggest baby power in spells relating to child blessings or in children’s rooms as the scent would not be overpowering for tiny senses and just remind you to vacuum up well after the work is finished.
Personal power, group power, incense, cord, singing, chanting and musical instruments, etc. used indoors or out as needed causes little trouble, other than drawing nosy neighbors on occasion.
The point being, just as with your spell crafting and ritual work, the only limit to casting a circle is your own imagination.