I got this Idea from looking for a simple DS game case made entirely out of duct tape, but couldn't find one I liked enough :p so I made this
Note: This is my first instructable, please comment on any error you may see in it
also, sorry for the image quality, but I think the images are good enough to get the point across
Step 1: Materials
1. Duct tape
2. Knife (or other sharp object) to cut duct tape
3. DS game cartridges (have as many as you want the case to hold)
Step 2: Cut
Create as many of these strips as the amount of game cartridges you want the finished product to hold (I want 8 cartridges to hold, so I make 8 strips)
Step 3: Wrapping
Then, fold the excess duct tape to the back, this makes the bottom.
Place on a surface that will not ruin the adhesive of the duct tape (Do not put it on carpet for sure)
Do this with each cartridge and strip.
Step 4: Aranging
Check over your design before you put them together, it is difficult to take apart.