Do you want a large heavy tripod for weddings or landscapes or macro work? Or is a small travel tripod all you want? It's hard to know without some knowledge of what you want it for!
If it's just a general feeling that you'd like to spend some cash and get some bits that might come in useful, I would say don't buy one. You will only bother lugging a tripod around if you know you need it. Otherwise it is just a big weight that gets in the way.
If you do want something serious, here are some tripod reviews:
http://www.techradar.com/news/photography-video-capture/cameras/best-tripods-and-camera-supports-15-tested-1046066
This is the only one that they gave the full 5 stars to:
http://www.techradar.com/reviews/cameras-and-camcorders/cameras/tripods/giottos-mtl9361b-1027720/review
For filters, are you talking about just a screw on UV or sunlight filter or do you mean special effects?
Some people like to have a UV or skylight filter on each of their lenses for protection. Some others claim that it adversely affects image quality. I've had a 50mm lens saved by a filter before and not noticed any big degrading of quality - but I do use high quality filters.
For a reasonable UV or skylight try the Hoya Pro filters, but for effects, Cokin is the king.
I'm not much into effects filters. A circular polariser filter can be useful (but expensive). If you do want a polarising filter don't buy a linear polarising one. Circular polarisers are the only ones which will work correctly with your autofocus system. Neutral density filters can be useful in bright light if you want to get slow shutter speeds for things like those ghostly waterfall effects. I would leave other filters alone for the time being.
For lens hoods, get the ones designed for the specific lenses you have. Generic ones are not particularly useful, and if they are too large they can cause vignetting.
For flashguns buy Nikon. The Speedlight SB-400 is a fine, lightweight and affordable little flash which will most people will find sufficient. If you want to go into zoomed, rotated, bounced flash the SB-700 is a good choice, but it is twice as expensive as the SB-400 and you might find it makes the camera feel a bit top heavy. Forget the SB-600 unless you can get it cheap or second hand. It is effectively superseded by the slightly cheaper SB-700 and I doubt you will need the extra features (or expense) of an SB-900 or SB-910.
If you decide to buy a second hand flash on ebay, stick with models which are in the current range. Older flashes like the SB-28 or SB-50 may look cheap, but they won't give full functionality with digital cameras like your D3100.
By the way, what word were you trying for when you typed "abduction"?