The duck feeding area on Dinton pastures Black Swan lake would often do bites. After the public had gone you'd see a carpet of bread crumbs on the lake bed but in the morning it looked like a hoover had been through there, not a crumb in sight.
Personally I'd avoid the pva bags to start with if heading straight to duck feeding area, instead I'd flick out a single with a light lead or a choddy. You don't want to spook any carp with a large splash from a bag as they maybe feeding still on the previous days bread etc. But as Yonny rightly says, on a day session it's all about finding them first. If they're not showing there will still be little signs. These could be small swirls on the surface, the odd bubble hitting the surface in a certain area or the more obvious signs of big fizzers or coloured water.