I haven't yet tried proper adult-baby diapers like Bambino yet, I just rely on store-bought ones; usually Boots' 'Stay-Dry Slip' (UK). However, as these aren't all that thick, I usually find that it feels a lot better to put 2 on at once, to get that wonderful bulky feeling.
Quite often I'll wear a smaller size underneath, for a tighter fit to prevent leaks, and a larger one on top, which still fits OK. Also, I usually poke holes in the outer skin of the inner diaper, so that wetness can get through to the outer one, increasing capacity.
Does anyone else regularly wear multiple diapers? Or are the high quality diapers thick enough for you.