Instrucables on making a half-size MKVII bag from Indiana Jones the other day. I've been using a crappy hiking bag to carry around my 3DS when we go out and about (like yesterday at the Grand Rapids Comic Con), so this would be an excellent replacement.
Because my sewing skills are still pretty beginner, I opted to use an old pair of khaki pants as opposed to spending money on good fabric. That way, if I ruin anything, I'm not really out anything (except time).
So if you're looking at the top of the pattern in the instructable, the dimensions I used were actually 6.5"x5" for the top square, then 7"x5" for the next square. The bottom portion was also expanded to 7"x5" (and 7"x1.5" for the sides)
Now to decide on a strap and a closure!
Update: Mini-Satchel, Now With A Strap!