This is a Bento Box.
A Bento Box is a type of meal box that can be packed for lunch. However, it is not a lunch box (as those generally fit drinks & are meant for bagged food) This is meant to hold a little 'setting' of food like rice, veggies, fruits, meat & etc. Sometimes these are set up in a decorative way inside, because the lid is snug. 

You can see many festive looking bentos in a search. What IS surprising is that with how common a Bento Box is in Japan, that there's not more Sonic themed ones, and that it took this long for this one to show up. The art here is obviously the "Sonic Screen Saver" art which was very quaint and classic. This has a scene from it, with little egg-o-matic Eggman in the background and the 'dont waste your precious time' quote on the street area.
The interior seems to have 1 separated area (so sauces etc. don't mix) & an interesting plastic item. What is the clear plastic thing toward the right side? It doesn't seem to be a spoon due to the odd shape. You can write in for credit if you know what this thing is.