Originally Posted by Rockfish

If you are not very mechanical I'd second the LBS recommendation. Most shops can order pretty much anything, and they can install things for you if necessary. If you don't need install help, then you could save a few bucks buying online.
Fenders from SKS or Planet Bike are good and not too expensive if you shop around. Make sure you get wide, 26" ones. V-Brakes can be a pain, but you can run the fender over them, as above, trim the fender to be a bit narrower where they go through the brake arms, or just let the brakes squeeze the fenders when you apply them.
I have Topeak rack and bag and like them. As noted, any bag will work on the Topeak rack, but the Topeak bag is designed to only work on their rack. Make sense? The Topeak bag is great if you need to take the bag on-and-off a lot - like every time you get off the bike. If that's not important to you, then any bag will work fine. Racks are about $30 on amazon, etc.
I would also give a strong +1 to replacing your knobby tires with smooth tires that have a flat-prevention layer. They roll much better, and save you repairing a flat constantly. You should be able to get a pair of tires and tubes for $50 if you shop the major online sources for a deal or sale.
Hope this helps. Good luck!