Many outdoor activities require so little equipment it will all fit in a big pocket or small daypack. Some others need a bit more, or by the time you get everyone's little bit together, it won't quite fit inside your car. Carrying stuff on the roof of any vehicle is possible, but just dropping it up there is not a good idea. The sheet metal is pretty thin and the paint even thinner. So, you'll need a rack that attaches to the top, back, or hitch of your vehicle.
Roof Racks
Quite a few vehicles sold today have some form of rack from the factory, and unlike 'luggage' racks of the past, the siderails and crossbars will have weight capacities similar to aftermarket racks, around 125 pounds. Most rooftop accessories are now being designed to attach to the wider 'aero' shapes of these systems, so you're ready to go.
However, if you have only the siderails, you will still need some form of crossbar to keep the load off the roof. The 'factory' bars will be the best match for the overall look of your car and be quieter than most aftermarket products. Most new-car dealers will be able to install the factory system, but keep in mind it might be a special order item, will only fit your make, model, and year, and could have a pretty big pricetag.
So, what about an aftermarket rack? The basic setup is two pair of towers or feet that attach to the car and a crossbar for each pair. From there you might consider a locking system to keep someone else from removing the rack, and a fairing to reduce wind noise. If your vehicle already has front-to-back rails, the feet will attach to those quickly and easily with a fair amount of adjustability.
For 'naked roof' cars and trucks, raingutters on cars were ubiquitous at one time, and allowed the same tower design to work on many vehicles. Today the towers or feet are designed with a system of rubber pads and clips or brackets so they match up with the roof shape and clamp onto the door opening with the most security and least chance of marring the finish.
The two main brands, Yakima and Thule, (pronounced 'too-ley') have experts who get hands-on with new cars and develop a specific fit for each. The only tools involved will be a small allen wrench (hex key) provided with the rack. Most roof rack dealers will provide installation, but the instructions included are very clear and with a little patience, you can install it yourself in about an hour. Because of wear and safety concerns, sport rack products are not returnable after they have been installed, so be careful.
Once you have crossbars installed, the options for carrying almost anything are very broad. Boxes and baskets can expand your cargo space, and special carriers for bikes, boats, and snowsports gear will make loading and unloading much faster and more secure.
Boats
For transporting your boat, you may get away with just flipping it over and strapping it deck-down on your roof rack crossbars. Gunwale brackets that hold a canoe horizontally will increase stability, as well as lines from the bow and stern down to the vehicle will give the driver more confidence.
Some boats don't have much flat space, so some form of kayak cradles will make a big difference. By matching up with the hull shape, the cradles will hold securely with minimal effort, and after the intial adjustments, loading will be much faster with less hassle.
Pickup Trucks
You probably bought your pickup because it can carry a lot of stuff. Why would you need a rack? The most popular answer is that you bought a canoe or kayak, and it won't quite fit in the bed without extending off the tailgate. Be careful about propping the boat on the cab with the other end down in the bed- it will catch air with disastrous results. Better to carry the boat parallel with the ground or with the bow lower than the stern. This can be achieved with products that clamp to the bedrails or mount to the trailer hitch. Once you have an above-the bed solution, you'll have more room for all the other stuff. Just remember your truck is even taller now, so mind the low-clearance signs.
Rear of Car
Sometimes putting your bike on the roof just isn't going to happen. Either for convenience or safety, you may want to use a rear of car carrier. These will hook to the trunk or hatchback with metal clips and straps that are carefully tensioned to keep the load from shifting as you drive. By carrying the bikes below the roofline, you can worry less about low branches or barriers, but keep in mind that when loaded, you will lose access into the rear of the vehicle and have reduced visibility. Rear of car products generally have much wider fit compatibility, but be sure to check with the manufacturer before you buy.
Hitch Mount
If you have a hitch receiver already mounted, several bike and cargo options can mount there and provide very easy access to your stuff. The better products will swing out of the way to provide access to the back of the vehicle, but all will make your car longer, so remind yourself and look twice when backing up.
Strapping it down
Outdoor equipment and boats are pretty durable if treated properly. When securing anything to your rack, keep in mind that the tension on the strap should be just enough to keep things down, and the accessory or padding should stabilize the load side-to-side. Roof rack companies sell and encourage the use of cam buckle straps and not the ratchet-buckle style, which can create too much tension and might crease the hull or worse.
Follow the Directions
The roof rack brands work very hard to make sure your cargo is safe and secure on your vehicle, and their websites and installation instructions are very clear about what will fit and what won't.
It is very important that you use only the exact parts described for your fit, and if the manufacturer doesn't list your vehicle as compatible, trust them. For example, if your Yakima installation calls for Q99 clips, that means Q98s or Q100s will not work. Both Yakima and Thule offer excellent fit systems on their websites, and sometimes the result is 'No Fit.' Believe it. If you have any questions at all, call your local installer or the brand directly - they have experienced people who can help you, if you follow their advice.
Glossary
Foot: Term used by Thule to describe the part that mounts directly to the car and holds the crossbar.
Tower: Term used by Yakima to describe the part that mounts directly to the car and holds the crossbar.
Crossbar: Steel bar that attaches to towers or feet and provides the load acrrying capacity of any roof rack system.
Q-Clip: Term used by Yakima to refer to the rubber pad-and metal bracket part that allows the tower to connect to the car. Q-Clips have been designed to fit almost any car.
Fit Kit: Term used by Thule to refer to the rubber pad-and metal bracket part that allows the foot to connect to the car. Kits have been designed to fit almost any car.
Fairing: Flat plastic panel mounted to front crossbar to reduce wind noise.
Lock Core: Locking element installed in towers, feet, and/or accessories to provide security for your rack. Designed so one key will fit all cores on your vehicle.
Headache Effect: Possible result of installing crossbars that are too long for your vehicle in an effort to gain room for more gear. Felt acutely when exiting said vehicle and standing up into the crossbar that extends out over the door opening. Easily avoided by following manufacturer's configuration for your car or truck.