Johnny,
Lump charcoal is definitely the way to go. I've tried a great variety of fire sources in my SNP Pro. Depending on what you're trying to accomplish you will want to stick mostly to hardwoods like oak and hickory but be careful how you use them or you can get too much smoke. I have a fire pit and use it to produce coals for cooking. There are some posts in the forums that explain how to produce your own coals with simple devices you can make easily. There are a few brands of bagged lump charcoal, though the names escape me. I've used them before but it's an expensive way to go. You can find pre-packaged firewood bundles at grocery stores and Menards/Lowes that are usually red oak (depending on where you are) or look in your local paper's classifieds for firewood suppliers and call them to see if they'll sell smaller quantities of oak or hickory. Quick and easy would be Kingsford with mesquite but, again, watch so you don't get too much smoke. I typically use charcoal briquettes to keep the heat up a little (I've found the cheaper the better because they have more lumps of chacoal in them) and well soaked chunks of hickory. I try not to use mesquite with charcoal because I get billowy smoke from it and it gets a little overpowering. Better to use mesquite with lump charcoal or oak and use it sparingly. Remember: Thin Blue Smoke. Long smokes are really easy with the SNP Pro as you can control the air flow so well. Just make sure to put a baffle that sticks out into the cooking area to help regulate the heat and smoke. I used simple sheet metal that hangs off of lengthened fire box mounting bolts. (Stay away from galvanized). I hope you have great successes, as I have, with your Brinkman, it's a great way to learn about proper smoking and a stepping stone to more advanced units and methods.