as for killing animals, im camping on a farm so i will take my slingshot and ask them about hunting there (there will likely be bunnies and pigeon which they wont want, and rats, but i would prefer my gun for anything but bunnies), but really you need to get permission from the landowner.
there are some nice big lakes, and of course the sea, so you could fish. if you dont want to take a rod then search the forum for "hobo fishing reels". the guys on here make them beautifully out of wood, but the concept works with anything round, a stick, a tin can etc. you will need a fishing license for the freshwater fishing. you can eat pike, eel and perch as well as trout and salmon, so you are bound to find something edible.
you may also want to try collecting some shellfish from the beaches if they are appropriate (if they are polluted, which is unlikely in wales, then dont eat muscles, limpets are fine though). look through the "lovely grub" forum for ideas.
not to be patronising, but are you sure about a wild camping trip as your first bushcraft outing? would it not be better to have a definite place to stay, like a proper campsite (or the place i am going: LL55 4SR ) and then go out during the day to find nice wild camp spots and spend the days there with a fire going or whatever and then go back to the place you know you arent going to be kicked out of in the middle of the night.
gain knowledge of the area first, see where you can wild camp and what the best places are, then you can go there next time knowing exactly what you can do legally.
have fun anyway, ant take lots of pictures