These include many seedpods, cones, grain, grasses, and berries found in the garden, as well as in fields and along roadsides. Here are some specific examples.
Berries add great color and texture to an arrangement. Rosehips are a great example. This somewhat spherical fruit of the rose, usually red in color, is seldom allowed to develop on our modern roses. However, the old-fashioned shrub types, such as the rugosas, bear them abundantly. The rugosa rosehips are large (1/4 inch) and bright red.
Other berries to try include cotoneaster, crabapple, bittersweet, hawthorn, euonymus, firethorn, viburnums, and more.
Interesting stems and twigs add texture and height to an arrangement. Curly stemmed plants work well for this. Examples include contorted hazelnut and corkscrew willow. Uniquely shaped stems of any kind will work.
Grass flower heads add softness. If you have ornamental grasses, these work great. You can also use the "weedy" grass flower heads that is abundant in our landscape. Examples you might look for include Bristly foxtail, Fountain grass, Northern sea oats, Pampas grass, Plume grass, Quaking grass, Spike grass, and Squirrel-tail grass.
Grains such as wheat, oats, rye, or even sorghum work well too. Other seedpods to try include poppy, lotus, cattail, dock, honesty (money plant), iris, lily, milkweed, mullein, and Queen Anne's lace.
You might still find some old flower heads in some gardens that are useable. These might include Baby's breath, Bachelor's button, Bells of Ireland, Cockscomb, Globe amaranth, Larkspur, Scarlet sage and blue sage, Sea lavender, Statice, Strawflower, and Yarrow (yellow varieties best).
I encourage you to make a table decoration for your Thanksgiving table this year. Gather natural items and make a dried arrangement or purchase some fresh flowers to go with it. For a more traditional look, put the plant materials in a cornucopia or flat basket. Have fun and enjoy!