There are many different variations of this that you can make. The photos here are of a doll's house themed case so I used carpet tiles, wallpaper and doll's house furniture to make a home for peg dolls but you can be far more generic in your creations so that they can have many different small world uses. Paint the lid with a more general design (for example 'What's in the box today?' 'Small World Adventures' , etc then let your imagination roam. See below for some ideas
Weather Box Use green felt or fake grass in the base and blue felt inside the lid. Then add felt weather items such as rain clouds, snow, sun, rainbow, gusts of wind, etc with Velcro on the back. Add dolls with different clothes options according to weather.
Nature Box Add fake grass and a selection of different natural materials. Add enhancements according to your topic e.g. mini-beasts or hibernating animals
Off to the Beach Paint the inside lid blue and paint the base yellow. Add real sand and tiny beach themed objects
Dinosaur World Add lots of sticks and stones. Add brown 'mud' playdough and pop in some dinosaurs
Celebration Box Fill the box with a celebration theme - a Christmas living rooms, Santa's workshop, a Nativity scene, an Easter Garden, birthday decorations, etc
Challenge Case Use it as a mini me home and put a photo or model of each child in with a challenge for each child. Can the class get used to looking for their mini me and completing their weekly challenge?
Use it as a Suitcase! Have a virtual journey around the world. On day one fill it with items that hint you are off on your adventures (passport, plane tickets, map, binoculars) then each day change the contents and learn about a different country.
Having a bit of a clear out or car boot rummage this summer?
Why not find an old suitcase (or any solid bag or box with a hinge) and make a new small world environment?