We ordered a storage cube set in black from somewhere last year and set the larger one in the area between the driver and passenger seats up front. It was about 18" square, the smaller cube fit inside and didn't have a removable top or storage. I think they were $60 or so, for the set. Both were of faux-leather, had nicely cushioned tops and of good quality. I just Googled "storage ottomans".
It was perfect for us. The top flipped over, had handles and became a tray. I badly needed someplace to put the laptop, phone, reading glasses, etc., when we were driving, and also liked the extra storage space it provided. Our sweet Lily, however, (who we acquired later) would have no part of something between her and her people, especially me
, and would simply jump over it and into my lap. We now leave it behind.
We have two of the sofa-sidekick tables in our stick house, which work well for limited uses. They are a bit unstable, though, if not tucked under a couch or chair, and can topple over rather easily.
Personally, I'd recommend the storage ottoman with a tray lid. When not using it as a table, you can prop up your travel-weary feet and cover up with a blankie you have stored inside.