BA offers preflight dining to "appropriate" flights (and that meal is very nice indeed, particularly at JFK), as such BA doesn't feel it necessary to stock decent food in any of the JFK lounges. You can get chips, apples, cheese and sometimes sandwiches (small tea sandwiches, nothing to substitute for a meal). It is meant to be snacks with your drinks, or to kill time, and not to feed you. As for the shower upon arrival, the arrivals lounge at JFK is not yet built so there is no access to showers unless you are in transit to another flight operating from T7.