Don't worry, if you're like most of us, you'll end up buying all the things you listed and more... :-)
No one yet has said why you'd need this or that (at least when I started to write this), so I'll try.
As to what to get first, it depends on what kind of photography you're enjoying at the moment:
- If you take lots of pictures outdoor and live in a sunny area, then a polarizing filter may improve your pictures: when used correctly, it will give you beautiful dark-blue skies while keeping whatever is in the foreground properly exposed. Keep in mind that the effect will be maximum when used 90 degrees to the sun, and you'll get almost no effect if the sun is right in your back or in front of you. (a polarizer can also be used to reduce reflections on water or shiny surfaces, and can sometimes increase color saturation)
- If you like taking pictures at night/evenings while walking in your city (you know, when you're forced to use high iso / low shutter speed...) then at one point you'll want a tripod. Using a tripod would permit you to use longer shutter speeds without fear of camera shake. Main benefit: you can now increase your depth of field (close down your aperture, use F8, F11 etc...) now all of a suden YOU can decide the amount of "in focus" you want in your picture. At the same time you also have the choice to reduce your iso setting, which will result in less noise in your photo. Slow shutter speeds will also give you interesting effects like trailing car lights, "ghosts" passersby etc..
I've talked about night shots here, but lots of landscape photographers use tripods all the time in daylight...
- If you take a lot of picture indoors, at parties, family events etc, then an external flash may help: you don't worry about low shutter speed/camera shake anymore, you can balance your subject exposure with the ambiant light, you can create effects etc etc. External flash with tilt/swivel is a must as it allows you to bounce light to walls, ceiling etc, thus giving you a softer, more natural lighting.
Some may argue that you don't need flash if you can use a fast prime (those lenses that open at f1.4 or 1.8). I think it's a question or preference. I use one or the other depending on the circumstances, or the mood I want to convey.
Oh, one more accessory I almost forgot :
- if you don't have an unlimited budget, then a Pentax M42 to K-mount adaptor will be your best friend... it will open to you a whole world of (relatively) cheap but high quality second hand lenses :-) (think Takumar, Carl Zeiss Jena, Vivitar etc..)
Those are the first items that came to mind and I don't want to make this post too long so I'll stop there for now.
Hope it was usefull.
Don't hesitate to ask if I have been unclear on certain points.
Oups, I just re-read your post and saw you've already ordered a tripod... oh well, maybe it will help someone else