I'm not so good with the eating and drinking in the City Centre, I did most of that in the outskirts where I lived. But from what I know here's my 2 cents: There are loads of bars around Temple bar. It's pretty famous for stag and hen parties. This may not be what you're looking for though. For the best pint, or best "Irish" bars there's probably better. I'd put my money on someplace like dame street or grafton street. There's some really nice little pubs on dame street and also off the side streets of grafton street.
For food, I'm stuck. It's been quite a while so I wouldn't know where to recommend.
Also, I'm thinking the Samuel Beckett bridge is a bit off the beat and track.
So, here's one option: A walk that could work for you with some nice photo opportunities.
North of O' Connell street, walk down O' Connell street. Get in the Spire, plus other things, like henry street, great for the stalls if you get them on the right day (can't remember what days now!). Great for street photography too. Go right up to O'Connell bridge. Cross O'Connell bridge. Even around here there are loads of photo opps to be had.
Now, at this point you could choose to jump on a bus west bound and go to the Guinness brewery. I know this is bus 123 from O Connell street/Dame street, and it's 10 minutes on the bus. I have never been though, but seen some nice shots of there and abouts.
If you choose to go I'd probably get a bus back down Dame street again and aim for temple bar next. Some good street photography here.
Next I would advise aiming for Trinity Uni and after that on to Grafton street.
Go through Grafton street, look left and right all down the side streets. Loads of photos, places to eat, people to photo, places to shop, more stuff to photo, pubs to drink in, until you end up to stephens green. You could take a quick peek in stephens green if you wished too. Could find a photo I never did!
But I wouldn't go any further than that.
You could work your way back using Dawson street and using the side streets again for some nice shots.
If you ever get lost aim north for the liffey!
There's loads of other routes, but that should get you started.