Start domestically, something simple, but realistically any "wide open" flight (especially coming home!) is worth considering. Just have a few backup plans, and remember that anything can happen (if a flight cancels, people will have to rebook. If you go to Honolulu, you'll get a pile of nonrevs within 24 hours of departure - both directions). Did I mention that HNL is a terrible starting point? Not that you mentioned that, it's just that places you want to go, other people probably want to go to as well.

Without knowing what kind of things you're interested in, I'd suggest my hometown: MSP. Take a train in one direction, and you're in downtown Minneapolis. I think they also opened up a line to St. Paul, otherwise it's coming soon. Take that train from the airport the opposite way, and you're at the Mall of America 15 minutes later. Good day trip, though you may want to stay overnight so you have more options to get back. Sometimes those hub-to-hub flights can be tricky (MSP and JFK are both hubs for DL, but PHL isn't) since they're commonly used when people need to be rebooked, but they also have the advantage of intermediate stops. If JFK-MSP looks hard, consider JFK-ORD-MSP, JFK-DTW-MSP, JFK-BOS-MSP, even JFK-PHL-MSP. Or others. If you're lucky, you may even keep the same plane on your layover. Hop off, stretch your legs, and hop back on (once you get a seat assignment). If you need inspiration, check the wikipedia page for any airport, and scroll to the airlines and destinations section.

And just remember: When in doubt, first flight out. Especially flying *from* a hub, would you rather be on the flight where passengers misconnect from an earlier flight, or would you rather compete with them for seats later in the day?