I suppose it is really very hard to get ones head around how you stock up a sail boat for a transatlantic crossing. By the time you get to the Pacific you will find it easy. All over the world there are now supermarkets, except a few South Pacific Islands. You cannot always get exactly what you want but the basic items are always available - a crew of 3 or more is going to fill at least 2 supermarket trolleys and the bill will make your eyes water but remember it is food for several weeks!
Really it all works on number of days times number of crew for water, breakfast, lunch and dinner plus snacks.
Although I suppose most boats will do the Atlantic in 25 days or less. The prudent action is to plan for 30 days or more if you think that's right for your boat - always have a few days more than your estimate.
WATER. I think it is important to split the drinking water into several containers in case one gets broken or contaminated. You can go without food for up to 10 days and still survive - After 2 days without water it is problematic so water is the most vital concern for a long offshore passage.
I now have a water-maker but even so, I always want to have enough water in the tanks and jerry jugs to be able to make the passage without the water-maker working - I then use the water-maker to make fresh water for washing etc but if it did break, we could still get there safely. On ocean passages I carry 3 x 6 gallon jugs of water on deck strapped to the guard rail. (Bottled water is of course readily available everywhere in light weight plastic bottles.)
How much water? I think you need a minimum of 3 litres per day per person per day. I also carry at least 1 & 1/2 litres of uht milk per day per 2 people for breakfast cereal, coffee, tea and it is nice to have some bottled drinks although I mainly rely on 'CoolAid' - or similar powdered flavours to mix into the water for drinks. Neither it nor its containers weigh very much.
On ocean passage I allow crew 3/4 a litre a day each for teeth washing and possibly to wash their hair every few days. I turn off all the electric pumps and only allow fresh water to be drawn on the manual hand/foot pumps.
Before the water maker, I issued each person with an empty 75 centilitre plastic bottle to fill and do what they like with each morning - the remaining two plus litres was drunk or cooked with as required - seemed to work out OK -
If you have a crew of 4, on a slow transatlantic of 30 days, each drinking 2 litres and washing/drinking the 3rd 1 litre - that would require 360 litres about 80 gallons - this is more than the average water tank in a boat so you will have to purchase some plastic jerry jugs and tie them to the rail. Of course it will rain sometime - probably - so a method to catch the rainwater and transfer it to containers is really useful. Mind you normally the smaller the boat the smaller the crew.
If you carry UHT milk at the rate of 1 liter per 3 persons per day for 4 crew that's 40 litres and should be more than enough.
Works out like the water:
Breakfasts x 4 crew x 30 days
Lunch x 4 crew x 30 days
Dinner x 4 crew x 30 days
Night watch biscuits/snacks x 4 crew x 29 nights
Bread - baking bread in the oven is very easy and delicious. 1/2lb of flour will make 2 small loaves. You will possibly need to bake every other day if you can stop the crew picking at the freshly baked loaves so for this imaginary 30 day passage with 4 crew you need 7 lbs of flour + dried yeast sachets + olive oil + salt in place of butter.
Breakfast - It is easier if everyone has similar tastes in breakfast cereal - One thing you should never do is to bring cardboard into the boat - cockroaches lay their eggs in cardboard boxes, are horrid friends and difficult to get to leave... so take the cardboard off the cereal packs - saves weight and stowage space - how many cereal packs? well I think a cereal pack lasts one person about 4 - 5 days so 6 per person per 30 days x 4 = 24 packs cereal.
Eggs. Depends if you are into making cakes - obviously you need some eggs - good for salads as well. the cardboard packs are cockroach dodgy but the plastic packs fine - Eggs keep very well indeed . You really do not need to varnish them or cover them in Vaseline - just stow so they don't break BUT you must not buy eggs that have been frozen or chilled - these do not keep well at all. Same applies to veg, fruit etc - if it comes off the supermarket 'cold' shelf it will not keep.
I use Olive oil to cook and for everything you would use butter for, except on bread - butter or margarine will not keep except in the fridge and goes rancid if it melts. tinned butter is fine but very expensive. Olive oil is easy to stowed and the plastic container packing is light.
Lunches: - You are going to need 30 for 4 people and that's an awful lot. Rice is a wonderful thing - easy to stow - light clean containers and easy to cook roughly 1 cup of rice for 4 people cooked in 1 and 1/2 cups of water for 15 minutes-
Potatoes are fine - hang them in a net but they need cleaning and slightly more water - you cannot use sea water but if fresh water is short I believe 50 - 50 salt to fresh water is OK.
Spaghetti is a wonderful product for sailors as well - it comes in so many different shapes and styles and goes with everything - Tuna, Tomatoes sauces with corned beef, tinned vegetables etc It is filling and easy to stow - lots of Spaghetti is good and lots of toppings are easily available.
Tinned: tuna is a splendid product - easy to stow, cheap, lasts for ever. Can be served hot or cold with spaghetti, as part of a salad, or on bread. I carry lots of tins of it in case. Sardines are also ok but not so versatile. Corned beef is not the most exciting item in the world but will make excellent bolognaise sauce when mixed with tomato sauce, onion and garlic - if you don't tell the others what the sauce is make of they will never guess! A few Frey Bentos tinned meat meals are ok but really do not taste wonderful.
Snacks: On those long lonely night watches - feeling bored but loving the stars, moon and dolphins dancing in the phosphorescence most watch-keepers get the munchies and it is nice to chew away at biscuits with a cup of coffee or tea or whatever. I have a plastic box which lives in the cockpit at night filled with munchie things. There are normally 2-3 night watches per night and it is possible to go through lots of biscuits... Crews all have different tastes so it can include sweet things for the young and ginger nuts for the more mature or whatever.
It is nice to start the voyage with lots of fresh vegetables and fruit - buy in an open market but never off the cold shelves of supermarkets. I hang nets for stowing these items and once they are finished I just stow the net. If you have a deep freeze on board then life is really easy.
If you do have a fridge and or deep freeze consider how many amps they draw in a 24 hour period.
Consider how many amps you are pulling at night to run the navigation lights, gps, compass light, wind instruments, chart table light, vhs and autopilot if you do not have wind self steering gear. Then work out how long you have to run your engine each day to make up those amps.
Solar panels are great as you get further south but wind generators are less efficient when running down wind.
Fishing is good and works well if you put lines over the side. I normally tow at least two lines and in the Pacific and Indian Oceans and the Red Sea caught fish frequently enough to be almost self sufficient in them. Not so in the Atlantic.
Sometimes I have caught nothing for weeks on end but the main reason for not catching fish is not putting the lines over the stern. I do take them in at night as I don't want to drown some poor fish or have to land a monster in the middle of the night in the dark.