Jax:
The answer depends on why you are asking. If you are looking for general guidance the rules of thumb are pretty simple.
Things to Avoid
1. Greasy, oily, fatty foods.
2. Nitrates/Suflites and anything that messes with your capillaries
3. Caffine unless you are an addict -- Not drinking drinking your normal cup of joe (if it really is everyday) can cause headaches.
Things to Consider
1. Unflavored Oatmeal
2. Bananas
3. Apples
4. Oranges (unless you are suffering from an acid stomach)
5. Pretzels and other simple carbs
The other major factor to consider is hydration. It will probably effect your dive experience as much or more than what you eat! Drink up, eat right and enjoy!!!
If instead you are looking for info because you tend to get an acid or upset stomach when you dive, I have pasted in below the best post on the subject I have ever seen. SkipperJohn did a great job and deserves multiple "Thanks" for taking the time to write it!
P
"The stomach is a funny thing. I boat every weekend and after 30 years I've picked up a few good tips here and there which have helped a great many people. What you eat isn't just a concern in the morning, but all the way back to the night before. Watch what you eat. Avoid difficult to digest foods and overly acidic foods and greasy foods. Of course also avoid anything on your own personal list that may have been related to any discomfort in the past. This includes, of course, alcoholic beverages to most.
Have an easy breakfast. You should not consider those 3 slices that didn't get eaten the night before. Nor a deli greasy egg sandwich. Dry cereals-easy on the milk-and skim is better. Again, no grease. (Hard) Pretzels are your friend. They are a base (as in acid/base) and can help to neutralize excess stomach acid. They also hold off hunger which can add to the onset of seasickness (as mentioned above). And they help to soak up any liquids that may be sloshing about in your stomach. Speaking of sloshing. This is never a good idea. Ever play with a baby after a bottle of formula? While staying hydrated is a necessity too much of a good thing is never good.
If you need any seasick remedies, start the night before. Be advised, many remedies can cause cotton or dry mouth. I should think this isn't good when setting out to breathe very dry air for the next hour. Taking the meds the night before will help as this condition only lasts a few hours on the first dosage so this will occur while you are sleeping. Of course you should take more according to the manufacturers recommendations when you get up and if needed just as you step on the boat. Be prepared to be tired.
Natural remedies help. Ginger pills seem to work well. REAL ginger ale (most ginger sodas have no ginger in them). Also a bit of coke (many years ago parents gave kids coke syrup for nausea which was purchased form your local drug store). A good nights sleep is great if you can manage it.
While diving watch what you focus on. I have a friend who will get sick if he gets involved in any intricate task on the boat (such as tying knots). The trick on a boat is to stay focused on the horizon. While diving it may pay to look ahead once in a while and never stay focused in one position for too long.
Basically you need to try to remember what works for you and what makes it worse then devise your own plan.
Just remember the pretzels. They are like magic to some."
