I really like 215 Bistro (215 Dominion Rd). It is a 10 minute bus trip from the central city - and is on a frequent line so you should have no problems (or a good 45 minute walk from midtown). It is consistently the best value for money for a Euro style menu in my experience. Not super expensive.
I like Prego as a fun and easy place - the pizzas are pretty good . SPQR is a great people watching place especially if you grab an early evening street side table. You will see what constitutes style in Auckland! (both are on Ponsonby Rd which is very close to the city - you could walk it in 40 minutes or catch the Link Bus).
Tom Yum Eden (also Dominion Rd) is fantastic. The ambience is not so good - cramped and hot, best tasting Thai ever.
Tanuki Cave (below the Civic) is a nice place to hang out and because it has bar eating it will feel sociable even if you are on your own.
Landreth and Co on Ponsonby Rd is great for b'fast and lunch.
Monterey Coffee Lounge for lunch (in the nice little inner city suburb of Grey Lynn. This is owned by relatives so not completely objective!).
Mondiale in Grey Lynn (a 10 minute bus trip) is good for a glass of wine and great tapas. Reasonably priced and sociable. The servings are small so you can try a variety - the tuna is pretty good.
There is also the area in Elliot Stables which is popular for tourists. Central city and has a range of places - Spanish Tapas, South african sausage, Puhoi cheese etc. Very convivial atmosphere.
I've enjoyed solo meals at Soul Bar and Bistro, Kermadec, and Euro around the Viaduct Harbor. They all have online menus. I usually bring a book. On the less formal dining side you could try Food Alley on Albert St. Lots of good ethnic options--don't let the name fool you. You can also try the Occidental off Queen St for mussels and good people watching.
All good solid options - just posted a heap of stuff on Auckland in another thread. Places around the viaduct could be good running solo options as heaps of people watching opportunities! (Kermadec has a bar/casual dining area with bar stood seating looking out onto the viaduct area) I like to have a view when eating on my own! Had a good quick scoff at Zap 4 on Commerce St (Thai food) the other day for lunch.
Also, grab some of the excellent take away options (bakery chain Pandoros has a branch up the top of Parnell that does great filled breads, or grab some sushi from one of the many sushi bars) and head with a book to a place like the Auckland Domain (the park around the museum), or Albert Park (near the university above the Art Gallery) for a picnic.