I'd advise making up your own fishing kit. The survival type kits arn't that great to be honest. Lures, feathers, tinsel flashes and hokkai's etc are fairly useless in a fishing kit unless you have a rod and reel to 'work' them. Using hooks and bait with a handline is a far better option for sea or freshwater (as Ed says though freshwater handlining is not allowed). Just about every fish in the sea around the UK coast is edible. Some are of course better than others but they'll keep you alive in desperandum. Watch out for weevers (Echiichthys vipera, lesser weever) and greater weever (Trachinus draco) (which are exceptionally easy to catch) they have viscious poisonous spines on the gill covers and dorsal fins, which will cause extreme pain if they jab you.
http://www.glaucus.org.uk/weever2.htm I caught these regularly as a kid, and placed my foot (with boot on of course) on it's head to unhook them. They are edible though, especially the whitish, greenish belly flesh. The fish you are most likely to catch that arn't so tasty are pouting, ballan wrasse (strong jaws for prising limpets off rocks

.......I kid you not, thats one of their foods, so watch your fingers in a wrasse's mouth) and weever. They are all greedy and take bait easily, but they can be eaten if you're hungry enough. Other species that you're likely to catch from the shore with a basic fishing kit like a handline (ie not a beachcaster or special rigs) which are good eating are pollock, mackerel (summer and early autumn) eels, dabs, flounder, plaice. All perfectly possible to catch with a handline like you see the kids on holiday using.
My survival fishing kit would consist of,
An orange/red (kiddies) handline
A packet of various sized sea hooks (not too big though)
4 booms
a few weights 1 or 2 ozs is enough (you have to carry the fishing kit amongst all your other stuff remember)
A small spool of line of 6 - 8lb breaking strain for making traces off the booms.
Bait you can dig on site. Worms from the estuary rag and lugs, and shell fish from the estuary and sea shore, best are mussels, razor clams, limpets and most other shellfish will do the job. And live prawns if you can find some in the rock pools (hook through the tail to keep them alive and moving and more attractive to the fish) Crabs are good bait too, especially when they are shedding the old shell (peelers) and the new shell is still soft. If you catch a small fish (such as a joey mackerel) you can cut some of the white belly into 'small fry' shaped strips and use for bait too. In the old days fishermen used dried sole skin lures to catch bass and other fish. If you dry some fish skin in the sun it makes a good bait to carry around with you and will keep for a few days.
You can buy ready made up rigs from tackle shops which are useful to have in your survival kit. A 2 or 3 hook paternoster (8th rig down here)
http://www.fishingbig.com/fishing_tackle/fishing_rigs/sea_rigs/ is a good rig to use from pier or rocks which is where you'd need to fish with a handline dropping into deeper water. I've caught flounder from the shore by swinging the handline around and lobbing it out as far as I can and just leaving it for a while. All flatfish tend to grab the bait and swallow quickly before they realise there's a hook in it so it's very common to have a flatfish that has swallowed the hook.
I'd definately think about making up your own kit though, rather than using the ready made ones. You can be more specific with the componants, that really will give you the best chance of catching fish and no gimmicky type equipment.
PS always wear some kind of old plimsoles, deck shoes, old trainers or water type shoes like canoists wear etc when paddling in the sea and you won't have any problems with the weevers.