I learned the hard way about running out in the middle of a round and trying to resupply. You can't do it.
The fix is pretty simple-buy a bunch and don't worry about it. You can do this real easy when you're in the pro shop. After you click purchase and you get the "equip my bag" screen use your browser back button to return to the previous page. You can click "buy" again and the process can be repeated as many times as you want. Each time you do your account is debited and your bag is supplied.
Caution: the credit balance does not update if you buy this way so you need to make sure you have enough to keep going. Very convenient to pick up 3 or 4 sleeves at once.
YJ