I would recommend not buying ANY accessories and this is why.
1. Spare battery - the battery you have will last longer than any one shooting session you do. As a beginner, it's unlikely that you will go out and in one day, burn through a few hundred pictures. You might, but only if you don't think at all about what you're shooting which obviously is no good. If you go on a overnight trip that may be different. However, of all the previously mentioned accessories, this is the most sensible one, as running out of battery really sucks and a battery is relatively cheap and will be useful in the future.
2. Tripod - don't bother. At this point, you will only be interested in buying a cheap one and a cheap tripod is worse than none at all. Save your money, if you find yourself really enjoying photography, go out and buy a good solid tripod in a year or two.
3. External flash - again, don't bother. Personally, I think shooting with available light is plenty hard enough when you're starting. Adding a flash is extra confusion. You can use the one on your camera for now, it's not the best, but it'll do. No, I wouldn't use it at a wedding now, but with my first camera, I sure did.
4. Memory card - I wouldn't unless you plan on shooting RAW. Don't know what RAW is? See my last answer.
5. UV filter - again, theoretically useful, seeing as if you scratch your one lens, you're pretty screwed. But, a cheap filter hurts your image quality and a properly used lens hood gives pretty good protection also. A circular polarizer isn't a bad idea, but again a good one is expensive, a cheap one is junk and they're more useful for certain types of photography, that you may not be interested in.
6. 50mm f1.8 lens - maybe...in a few months. I agree with the previous poster that this greatly increases your compositional ability and enhances understanding of exposure. But, your kit lens is probably good enough for a few months.
The only "accessory" I would think you should buy, and it's not really an accessory is a book. Ideally, a few of them. "Understanding Exposure" by Bryan Peterson is a really good start. Ansel Adams first two books are also excellent. Also, why wait 2 years to take a photo class? There are cheap online classes, and many free online tutorials that are very good. In my opinion, when you can explain the following terms, it's time to start thinking about more equipment.
1. Aperture
2. Shutter speed
3. ISO
4. Type of light
5. Rule of thirds
6. 1/length of lens
7. Depth of field
Buy equipment when you realize that your current kit is limiting your creative expression, not when you want to own more stuff.
If in a year or so, you find yourself owning a lot of equipment, but shooting mostly on the green box, you've probably put the cart before the horse.