If the place you going is rocky, then you are likely to find limpets which are good eating like Xylaria said, I camp on the coast alot and like to take a few handfulls of winkles and whelks, and put them in a tub of seawater overnight so that they excrete all of the sand and crap in their digestive systems, then boil them for a few minutes and pick them out with a pin, nice dipped in vinager too. If it is sandy then you may be blessed with razorfish that can be found at very low spring tides and are identifiable by a keyshaped hole -
http://www.wirralseafishing.co.uk/images/razor1.jpg
Tread very lightly and sprinkle some salt in the hole and when they pop up grasp but dont pull, let the razorfish tire itself then it just slides out with ease. Another creature that likes sandy bottoms are cockles as well, I treat them the same as winkles and whelks to purge.
Another cool idea is to make use of all those plastic bottles that wash up by turning them into prawn traps, simply cut the top end off, invert it and sew it on with braided nylon (the type that can be found inside parachord) cut a little door for bait and retrieval, the smaller the better (so wont open under water, larger is flimsey), and stab hundreds of tiny little holes in it to it can fill with water easily and the scent can travel. Good bait is something oily like mackerel but anything fishy will do, even smashed limpet. Put a stone in and tie to a rock at the low tide mark, you may need make about 10 - 15 to get a good catch but they dont take long.
If you find some old broken lobster pots washed up, they are always worth patching up with bits of hazel and twine and putting out in rocky places, just remember to anchor them well at low tide, even wade out a little as they do tend to go walkies......