JFK is doable when the plan stays focused. The AirTrain gives you a predictable start, but New York distances can seduce a layover into becoming a race.
What to do with bags
JFK Terminal 4 lists baggage storage for travelers, with pre-booking or walk-up service and item inspection. If you are not using T4, add terminal-transfer time before treating storage as easy.
Leaving the airport
Queens food neighborhoods, Brooklyn near transit, or a simple Long Island beach/weather plan are more realistic than a Manhattan checklist. Use AirTrain plus subway or LIRR time both directions.
Getting back through security
Re-entry requires an onward boarding pass and acceptable ID. If you changed terminals, add time for AirTrain movement before security.