A couple million, if not more.
That's how many variations of grain salads exist, with, I'm sure, a couple million more to be discovered.
There is no right or wrong; pick a grain (quinoa, brown rice, bulgur, barley, spelt, etc.), add raw or cooked vegetables (yes, whatever you just thought of works), some protein (beans, beef, chicken, etc.) if desired and a little flavoring (olive oil, lemon juice, apple cider vinegar, unrefined sea salt, fresh ground pepper, etc.). Oh, you have some fresh (or dried) herbs handy? Add those as well.
Grain salads, which are a staple for me, can be made in bulk and make for a quick snack, lunch, dinner or meal when traveling. Pictured is a quinoa, (leftover) chicken thigh, kale and arugula salad.
Not comfortable throwing anything (or everything) you have in your refrigerator into a bowl and mixing? Go to a food market, see what is being offered in the prepared food department, get some flavor ideas and make your own for a third of the price (if not cheaper).
You want simple? How about quinoa, peas (frozen, that you've thawed), chopped carrot, parsley, olive oil, fresh lemon juice, salt and pepper? Wait, you have some asparagus from the farmers' market? Oh, and that telephone book from 2003? Chop that up and add as well.
To reiterate: use whatever you have!