If you live in New York City, and you want to go whitewater rafting with a group of your friends, then a perfect spot to visit is Upper Delaware River. This is within driving distance of NYC (and even accessible by train). So, if you're looking to ride the rapids, but don't feel like taking a big trip out west to the Colorado river, then it's a fantastic compromise. The other great thing about the Delaware river is that it's not too wild. The rapids are not so intense that you need to wear helmets, but they are fun enough so that it's not a boring drift down a placid river.
Where You Will Be Going
You are going to be heading up to an area called the tri-state. The major town on the NY side of the river is Port Jervis. If you and your friends live in the city and don't have a car, then you can get a train from Penn Station (the New Jersey Transit Line) that will run right into town. Otherwise, if your group is driving up, you can choose to stay on either the New York side, or in the Pennsylvania town of Matamoras.
There are multiple public access points to the river, which you can use if you and your friends have your own inflatable raft. If you don't own equipment, then you can hook up with a guide company that will outfit you. If you do plan on launching your own craft, make sure to use a public access point, and not simply trespass on private land.
Time Of Year To Go
The season runs from April to October. Be aware that even if you go early (April and May) the water will be cold and you might want to wear the same type of wetsuit protection that you would bring for September and October.
What You Need To Bring
You will need to bring your own inflatable raft unless you are going with a rafting company. If you and your friends are choosing to go during the warm summer months, and don't envision hitting the heavy rapids (such as Skinners falls which are up in the Narrowsburg area) and instead plan on launching at a lower point where the water is calmer, you can bring along an inflatable raft. These rafts are really great for the warmer months when the river is not flowing like crazy and you can make do with a good quality inflatable raft instead of one of the giant behemoths that the rental outfits use.
The other thing you need to bring along are flotation devices. Life jackets are essential if your group has little kids, but even adults should have life jackets. If you're crew is going to bring beers or other alcoholic beverages on the trip, then you want to make sure people are safe if they lose their balance and fall in the water.