I bought a Pelican 1200 which is great for being safe (padded) and secure (lockable).
But it is not always practicable when going out or just walking around town.

I went looking for the Nintendo Gameboy-Advance case that CrashLander recommended.
Not finding this in my local shops; I instead came across this one:
CaseLogic-DM2
I highly recommend it.

Although not as tight fitting as you are probably looking for;
this case is well padded, lined inside with a soft fabric, has front pockets
for phone and stuff, has grab strap that extends to shoulder strap, double
zippers that can be padlocked together.
This is ideal for someone who needs a little extra space for stuff, without
having to take a full rucksack. I use it for day to day at-work storage,
as it doesn't attract much attention like the Pelican case.
BTW, my answer to "what is that" (Pelican) is; "my lunch box",
"I have expensive tastes!" (locked!).

Hope this info helps someone.