If you have access to a vacuum former, or have constructed a DIY one to use, simply vacuum form a compact case to house your standalone electronics or arduino project.
I made this at techshop! www.techshop.ws
Step 1: Bill of Materials
Material to vacuum form (acrylic, pvc, pet-g, styrene...)
a mold (make one from wood, foam, rubber or whatever you want, but more easily and quickly, find a box, a tupperware, piece of wood, or anything that is around the size of your electronics.
a vacuum form machine
strong snips, a hacksaw, or a razorblade depending on the thickness of your material
a file or sander
an on/off switch
a drill or drill press with a bit the size of your switch's threads