When I make Gumbo, I use a product called Gumbo File', which are dried green leaves of the Sasafrass tree that are ground into a fine powder. I'm not sure if that's really something rare, but it is hard for me to find.
I like to use some Saffron threads when making Basmati Rice. They're a few dollars for a few of them and are the ?stamens? from crocuses. You get this tiny 1 1/2" square cellophane package with 6 or 8 threads in it for about $4.00. They may the rice yellow and have a delicate taste. You can probably use a few of them to make Tandoori chicken red (instead of red food coloring that's often used). I've never made Tandoori chicken since it requires a special clay oven. I love to eat it out!