I like the concept very much. You could put a tidbit in there talking about what happens if it was thoroghly searched (would they find patches or pockets they could use -- or can only the owner see it).

What exactly happens to the items when it goes into the pocket? If it goes into an extra-dimensional space, then it needs a disclaimer saying that other extra-dimensional spaces are bad and would have secret chest as the spell). If it really does involve the shrink item spell, that's a bit different -- and it should have a disclaimer saying extra-dimensional spaces are OK (and it would be more expensive because of it's uniqueness). Need to detail how long it takes to pull an item out -- I'd recommend it would be as a move action (see haversack)

I'd also suggest taking the +4 to hide checks up to a +5, so it is in line with other items... You also need to specify that it is a +5 competence bonus, to avoid it being broken by stacking.

Of note is that nothing is overwhelmingly powerful -- it is just a bunch of low level things tied into one.

We'd also need a cost -- and it would involve combining 3 items - Handy Haversack,a cloak of elvenkind and a ring of feather falling. Based on that, I'd put the cost at 10,900 (Cloak cost, double ring cost, double haversack cost).

Moderate Transmutation and Faint Illusion;CL 9th; Craft Wonderous Item, magic chest, invisibility, feather fall 10,900sp, weight 1lbs