Food is prepared by a food replicator for Starfleet members living on the U.S.S. Enterprise, as well as their children. Do you think that the school age kids on the Starfleet's flagship took their lunches to school in a lunch box?
Probably not, since their food was most likely produced as needed by the replicator. Unfortunately for us, replicators haven't yet been invented so we need something for our food. A Star Trek lunch box is the perfect choice!
There are a variety of sizes and designs to choose from. Most are traditional rectangular boxes, but I've also seen at least one that has a curved top, like the kind steel workers used in the early 20th century, and fabric bags. Some include matching drink containers, but not all, so look closely at what comes with a lunch tin if you also want a Thermos or water bottle.
As for the designs, there are many different images. As you see here there are pictures of cast members from the original series and the Enterprise, but there are also boxes with characters from newer shows. The most interesting containers that I saw on eBay were talking lunch boxes in the shape of character heads, such as a Borg or Ferengi!