I would buy as much tire chain as you can afford. They come in all shapes and styles.
Cable Chains - Are cheap, but not really useful on a 4x4 with aggressive tires.
Ladder Chains - are effective and economical. "V-bar" chains provide the best traction, but they might not be available for your tire size, and you will end up with truck chains that have a larger cross tread chain.
Diamond Chains - Are supposed to be the best. Easy to put on and provide great traction, but they are expensive.
Since you do not use chains that often, then I would get a set of ladder chains. Now 1 pair or 2. Again, get what you can afford, and what your truck can run. My Tacoma can only run chains on the rear due to clearence problems with the front brakes. My Jeep can run chains on all 4 tires.
Once you get the chains practice putting them on when its warm and dry. It makes it much easier when you have to them on when its cold and dark. Make sure that get them on tight, and check them after 10 min. of driving and retighten if necessary. Then check them on a regular basis.