Firstly take a set of mackeral feathers just in case. If mackeral are showing the skipper will probably stop and let everyone feather for bait.
Next the fish you can expect to encounter depending on where you go are dogfish (well lets be honest you will catch these and also conger, various rays, tope, smoothhound, Huss, whiting, and if your lucky a stay cod, or bass. If you fish within Swansea bay there are also plaice.
Rays and Conger are your most likely catch and these will take most fish baits, Frozen Mackeral and squid are the usual favourites. Use a hook trace of between 30lb and 70lb breaking strain (or higher if you are going specificcally for tope or conger as these have sharp teeth) about 3 - 4 foot long. I prefer a pennel rig (large hook tied to the trace and a smaller one sliding on the tace just behind it) as I think it presents the bait better, but a single hook is fine.
Hook size - I tend to use either 5/0 or 6/0 with the small pennel hook of 1/0. This will catch most thing as those hooks will be strong enough to cope with almost anything but small enough to catch round fish.
If your going for plaice (I don't know if these are about at the moment) use long thin traces with small hooks.
I would advise you take a small amount of worm (ragworm lasts longer on a hot day) just in case, and you could consider some sandeel (although I've never had much luck with these personally) but squid and mackeral is the main bait.