Accessories:

Are you going to ride in the rain? If yes, you need fenders. Also, a rain jacket.

Are you going to ride in the dark? If yes, you need lights. Also, reflectors and reflective tape. Go nuts.

Are you going to fall? If yes, you need a helmet and gloves. (Everyone falls btw). I'm stalling on gloves some while I figure out what I want out of them.

Are you going to ride for more than 20 minutes at a time? If yes, you need a water bottle and a way to carry it. (This doesn't mean you need to buy a water bottle cage right away... I refill a cheap 20 oz recloseable water bottle and carry it in my backpack)

Are you going to get flats? If yes (and everyone who rides will eventually answer yes) you need a spare inner tube and a way to inflate it.

I tend to forget about safety glasses. I wear regular ones and unless I'm doing serious metal shop or chemical lab stuff, they're usually ok. If you don't wear glasses, at least get *something* to protect your eyes.

All the rest of the accessories can wait til you know what you (and your bike) need.