#1 - The Parking Lot is Far Away
People on the ground may look far away when you're high above Six Flags New England aboard the New England Skyway--a high-flying cable car ride for all ages. But that's nothing compared to how far you are from your car when you park in the official Six Flags lot. In order to return to your car, you'll need to exit the park (have your hand stamped if you plan to return), climb tall stairs or navigate a long ramp to a walkway over Route 159, descend and catch a tram, then walk what may still be a considerable distance to your car. This makes returning to your car to fetch swimsuits or anything else you've left behind impractical: It's easily a half-hour proposition. The only alternative is to pay even more than the $20 it costs (as of 2012) to park in the main lot and to take advantage of preferred or valet parking.
While you may be able to save a bit on parking by leaving your car in one of the privately owned lots you'll see along Route 159 as you approach the park, keep in mind that you'll still need to walk inside the main parking entrance and cross the bridge over Route 159 in order to reach the Six Flags New England entry gates.