Most likely as what we know (and confirmed) as a vehicle's trunk space. It will hold slots (perhaps weight and/or size dependent?) which you can fill. Obviously this is limited. I can only image the same will work with carrying stuff around. You could only have so many pockets in your outfit, and I hope it will be limited to what you're wearing. If you want to sport swim shorts all year around, then you shouldn't be able to carry much more with you besides your wallet, cellphone, and your keys.
I'm just guessing here, but seeing bigger vehicles can move more, heavier, and bigger items, the same should apply to outfits. That and combined with stamina and intoxication.