There is an unmatched artistry inherent in natural elements. Flowers are the obvious go-to, but there are countless other simple choices that bring interest and character to the table.
Just look around the next time you are outdoors. If you live in the country, it's a no-brainer. If you live in an urban area you may have to be a bit more strategic... maybe visit a nearby park or raid your balcony pot garden. No need to complicate things. I have often placed a little thicket of just grass in a jar, or mounded moss from my yard in a collection of flower pots.
Foraged items are so simple, yet so effective. No matter where you live, foraging for natural things for your gathering will make it "you" specific. It will be a unique and one-of-a-kind representation of what you want it to be.