There are not many show-and-tell items beginning with an "x", but perhaps you have a xylophone that you could take along.
Depending on your class and what exactly you've been asked to do, you might be allowed to take along pictures instead of items. In that case, you could try an image of a Xerox machine, an image of an x-ray or x-ray machine, or if you have access to an encyclopedia you might find an image of a xebec in it.
quarter, quill, quilt
Xylophone is a show and tell item. It begins with X.
Yardstick and yo-yo are show and tell items. They begin with the letter y.
a mask, muffins preferably homemade and enough to share - double chocolate or apricot and cream cheese would be great - you could show and tell me and I help you eat them
van (toy) view master violets (have kids draw these) vacation photos or souvenirs
quarter, quill, quilt
A xylophone
Some items that start with the letter "I" for show and tell could be an iguana figurine, an ice cream scoop, an interesting book, or an instrument like a ukulele.
earthworm
box,fox clorox,ox
Yardstick and yo-yo are show and tell items. They begin with the letter y.
Xylophone is a show and tell item. It begins with X.
queen if you can get one.
Yardstick and yo-yo are show and tell items. They begin with the letter y.
Sandals, scarecrow, scarf, scrapbook, seashells, seeds, shirt, shoes, snowshoes, soccer ball, socks, softball, sombrero, stamp collection, storybook and sucker are show and tell items. They begin with the letter s.
a mask, muffins preferably homemade and enough to share - double chocolate or apricot and cream cheese would be great - you could show and tell me and I help you eat them
van (toy) view master violets (have kids draw these) vacation photos or souvenirs