Mussels are a good staple diet. The trick is to boil them in their shells and scoop out the rich orange flesh. The Mussel flesh can be frozen. Prawns and Shrimps are best used as live food. It is a common mistake to put too many into the tank as the increased stocking level can cause an oxygen depletion.
Limpets can prove too tough even after boiling, and are best used only in an emergency.
Tropical aquarists should be warned that introducing live food can introduce disease which can ruin the appearance of expensive coral fish. Winkles are the worse example. The often used statement that fish should be fed as much as they can eat in a few minutes can be misleading. There is no substitute for knowing your fish and their feeding behaviour. Some predatory fish are 'macrophagous' and will eat relatively few large meals.