Question 1.
Were there dedicated food preparation facilities aboard subs enabling baking of bread, cooking hot meals, refrigerators.
There was a galley, and compared to german U-boats it was quite roomy
Were there food freezers where meat & vegies could be stored ?
There was a cold storage area below the control room, abaft of the pump room.
Were there dedicated cooks for the entire ship or each watch ? how did it work 24 hours a day ?
Cooks did not go watches like the rest of the crew, but had to prepare the usual meals plus any extras ordered by the captain. During combat, cooks double as medics or additional damage control personell
Could crew raid the fridge for snacks ? Was there a pot of coffee on the brew at all times ?
You can't raid fridges on any warship, but maybe crewmembers could store snacks they bought ashore there, if they were pals of the cook. Access to the fridge would be limited to the cooks, inspecting officers and sailors who had their cleaning station there.
According to the "fleet boat manual", there was a huge coffee pot (20 liters) with a tap running 24/7 in the crew's mess. The wardroom did not have that, they had to order coffee from their pantry.
What sort of meals could be expected each day & how many times did crew eat daily ?
Usual meals are breakfast, dinner, supper, plus a midnight meal for the 0-4 watch ("pig's watch" in the german navy, how is its name in the USN?)
Did the menu vary ?
Not very much, I suppose. But then again, the Burger was not yet invented, so the menus might even have been more varied than today
Was there alcohol aboard ?.
The US Navy was officially "dry" and still is today. All other (non muslim) navies in the world allow alcohol in limited quantities. In the german navy, it is two beers per man and day. For special occasions, there is a rum call
Did the crew have access to coca cola or similar soft drinks ?
Would have taken too much storage space. I am not sure wether the notorious "bug juice"; non sparkling soft drink made from artificially smelling syrup in serveral "flavors" (colours actually) was allready around in WW2. If not, it was coffee or water. In the german navy, this drink is rumoured to contain "Hängolin", something of an anti-viagra
Was there a dedicated eating area ? Did crew eat off trays ? I imagine china would be something of a liability on subs
US subs had a crew mess (in contary to U-Boats), but it was definitely too small for the whole crew to eat there at once. If that was to happen (special occasion or so), benches in the torpedo rooms and quarters were to be used. The crew mess was for every enlisted rank group, the wardroom was for officers.
Usually, aboard a warship (in the US as well as the german navy), the officers eat from China (carefully stored) while the enlisted men eat from tin trays not unsimilar to those in hospitals. The food is the same for both, and usually it is fresher in the crew's mess as the galley is closer.
Did subs ever stop off at islands to trade for food with natives ?
No. Even in the 1940s western stomachs would have been unable to cope with that without any undesirable side effects
Question 2.
Showers .... were there showers aboard and if so how often were these facilities available to each crewman. I imagine with 70 people aboard a relatively small vessel it would require a lot of water
Fresh water was obtained by distilling seawater. The US system was quite capable even then. In U-Boats the freshwater was exclusive for batteries and cooking. In US fleet boats, the distillers produced enough to permit crew showers in regular intervals. I suppose there may have been "shower times" with long lines, and of course you could not exactly shower like Janet Leigh in "Psycho". If there was trouble with the distillers, batteries came first, so no more showers...
Question 3.
allready answered.