The standard fish should be cod, tho nowadays sometimes coley [a sort of pollock] is used as a substitute, being probably a little cheaper for the shop to buy. Plaice is sometimes offered as a slightly more expensive alternative. One can also opt for battered sausages, individual meat-pies, etc, instead of fish, in some establishments. A portion of cod & chips [i.e. french fries], wrapped in greaseproof paper & layers of thicker paper to retain the heat as a takeaway ['to go'] will cost about £3 - £4 at the moment, I think [c $6-$8]. The server in the shop will offer to salt and vinegar the portion if required, or to serve it unseasoned — depends whether one intends to eat it immediately al fresco, as finger-food while walking along, or to take it home & decant it on to a plate to be eaten with knife & fork like posh folk! — when of course one can add one's own ketchup, brown-sauce, Lea & Perrins Worcestershire Sauce, or whatever, to taste.