This is the other concern sitting in between "want" (which I do) and "need" (which I don't). Right now, I get away with wallet, phone and keys (left, right, rear jeans pocket)
If I got a manbag, I'd get that temptation of carrying everything including the kitchen sink around even though 99% of the time I don't need any of it. Certainly the 3DS would go in there (it's already often in my coat pocket, but less useful there in summer), pen, torch, maybe a bottle of water, some USB storage, some mints, etc etc etc. I dare say a small pony plush would hide in there as well

I would suddenly see a "need" for stuff that I've never genuinely needed to cart around any time in the past.