It was a mix indeed. I can remember Tales of Hoffman, GloWorm, and of course Alexander's Ragtime Band being recalled by passengers. The Quaker Girl was the big hit on the London stage and I believe something from that was played. Some of the Titanic CD's which are currently still on the market have done some of this homework and have produced a good representative collection of tunes.
As a matter of fact nothing. Music generally was not played during dinner. This was tried in the a la Carte Resturant, and originally in 1911 a small band platform and pino were installed there. I can't remember exactly, it was either too crowded or a nuisance, and the entire idea was done away with. The band stand and expensive Steinway piano was removed probably in later 1911 (very likely during the Hawke damage fix-up).
Titanic never had any such band stand fitted in the restaurant, and the string trio usually played after dinner. On D deck, in the 1st class Reception Room, the band played at afternoon tea from 4 - 5pm, and again after dinner was finished.
Another myth bites the dust!
But I still love this fictional scene in ANTR:
Musician: What's the use, no-one's listening.
Hartley: People don't listen when they're eating, but we play just the same. Isn't that so, Sir?
Andrews: They say it helps the digestion.
Hartley: Exactly, that's because it soothes the nerves. Right, number 24.
According to The Countess of Rothes, selections from "The Tales of Hoffman" was the final music played after dinner.
A year or so after the sinking, she was dining out and the feeling of cold and intense horror descended upon her. It was then she realized that the band was playing something from "The Tales of Hoffman".
The orchestra probably played light classical music as the passengers were coming down to dinner. There might have been only the pianist during the actual meal, and the orchestra joined together once more after dinner. I would have loved to hear them do a rendition of the Chocolate Soldier
'The Chocolate Soldier' was included in their standard repertoire, Jerry, but there was normally no music at all before or during dinner. For the locations and times when they did play for the 1st Class passengers, see Daniel Klisthorner's posting above.
The Chocolate Soldier was a very popular operetta of the time, containing many numbers. The band might have played My Hero, a waltz song for soprano, which was about the only part of it that endured. It's been recorded in modern times but I seem to have escaped hearing it for many years.