Ernie- 225.30 limit's you to one supply with additional supplies for special conditions and residential homes can't qualify for any of these special conditions. So at best we could run a multiwire branch circuit and call it one circuit like Greg says. And I agree.
I think the real intent is that all remote buildings get a panel, ground etc like an "HO guage service" but they make an exception for the guy who just wants a light and a receptacle in his shed. It probably makes a few less orange cords strung through the trees.
And the "obligatory" answer is minimum #8 cu. I liked that word"obligatory" so I thought I'd use it in the answer, must be the inspector in me. Could use #6 AL if you could figure out some way to keep it 18" above the earth.
Do you think Table 250.66 note 2 might allow you to use a #10 here ? Using the argument that the feeders to the subpanel are not Service Entrance Conductors and thus the "equivalent" size service entrance conductors to feed the load would be (is, in fact) #10.