We don't have any boats so there is no chance we can compete, plus of course our current quotas are unlikely to change so trying to export caught fish is a bad idea. We could farm them locally and once out of the EU the quotas can be renegotiated as we build a fleet. Alternatively we can buy from further abroad.
Steel we are buying it all from china anyway so long as we can sell premium steel products (we can't produce cheap steel because of cost basis) we are probably ok.
Telecoms we lost that years ago.
Business services - maybe.