When I moved to this farm from New York City, I didn't even know what these were:
Now I use these food covers daily, from roughly April to September. There are flies everywhere on a farm, and I leave eaten-off-of dishes out all day, re-using them for each meal, so that I have less dishes to do at the end of the day. (Saves both water and time.)
The food covers we have are from the local Walmart, cheap and junky looking. For something I touch multiple times a day, I'd prefer something nicer. Here are what some classier versions look like, and cost:
This bamboo version ($20) is nicer than plastic, but the downside is that you can't see what you're covering.
This straw unit is handmade by artisans in Burkina Faso, and has slightly better visual transparency. They cost a whopping £46 (USD $57) for one. I might pay that if I thought the artisans were getting all of the money.
My favorite of the bunch is this woven model ($30 for one, $50 for two) made in the Philippines. It has a handy feature most of the others lack: It collapses flat for storage.